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Structural and interactive relationships between intertidal Fucus populations and associated faunal assemblages Nassichuk, M. D. 1975

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STRUCTURAL AND INTERACTIVE RELATIONSHIPS BETWEEN INTERTIDALFUCUS POPULATIONS AND ASSOCIATED FAUNAL ASSEMBLAGESbyMichael David NassichukB.Sc., University of B.C., 1972A THESIS SUBMITTED IN PARTIAL FULFILMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF SCIENCEin the DepartmentofBotanyTHE UNIVERSITY OF BRITISH COLUMBIAFebruary, 1975We accept this thesis as conforming to therequired standardIn presenting this thesis in partial fulfilment of the requirements foran advanced degree at the University of British Columbia, I agree thatthe Library shall make it freely available for reference and study.I further agree that permission for extensive copying of this thesisfor scholarly purposes may be granted by the Head of my Department orby his representatives. It is understood that copying or publicationof this thesis for financial gain shall not be allowed without mywritten permission.Department of BotanyThe University of British ColumbiaVancouver 8, CanadaDate March , 19751ABSTRACTIntertidal populations of Fucus at two sites along the BritishColumbia coast were investigated in an attempt to establish relationships between various structural components of the alga and associatedfaunal assemblages. Experimental field and laboratory techniqueswere utilized along with a sampling program designed to monitor temporalvariation in faunal diversity and to determine the role of algal complexityin the formation and maintenance of associated animal communities.Algal structure was shown to be correlated with faunal diversityalthough other factors, i.e., Fucus height diversity, were more stronglyassociated with faunal diversity at certain times of the year. Thediversity of the fauna associated with Fucus differed between the twostudy areas and possible reasons for the differences are discussed.The factors controlling the lower intertidal distribution of Fucuswere examined through field and laboratory experimentation. Biologicalinteractions appear to be of primary importance in controlling the lowerdistribution of the alga.11TABLE OF CONTENTSPageAbstract iList of FiguresList of Tables viiAcknowledgements viiiINTRODUCTION 1(a) General 1(b) Selected aspects of the biology of Fucus 4MATERIAL AND METHODS 6(a) Description of study areas 6(b) Data analysis methods 8Cc) Bowen Island sampling techniques 10Cd) Fucus transplantation experiments 12Ce) Transplantation of structurally variable plants 13(f) Fucus density effects 13(g) Littorinid and limpet growth experiments 14(h) Fucus growth measurements 15Ci) Investigations of factors affecting the lower 15intertidal limits of Fucus(I) Pisaster—mediated mortality 15(II) Hermit crab grazing 16(III) Balanus—Fucus competition 17(j) Lighthouse Park sampling techniques 17(k) Mytilus edulis—Fucus competition 17(1) Limpet marking experiments 18Cm) Laboratéry experiments 19(I) Littorina and Acmaea behavior experiments 19111(II) Idothea selection experiments 20(III) Pagurus grazing experiment 20(IV) Pisaster—Fucus interactions 21CV) Detachment of Fucus by Nytilus 21RESULTS 22(a) Bowen Island and Lighthouse Park Fucus population 22characteristics(1,) Bowen Island sampling 23(c) Fucus transplantation results 27(d) Density transplants 28Ce) Littorina and Acmaea growth experiments 30(f) Factors affecting the lower intertidal limits of Fucus 30(g) Hermit crab grazing 31(h) Balanus—Fucus competion 32Ci) Plant growth studies 32(j) Lighthouse Park sampling 34(k) Mytilus—Fucus competition (Juvenile Plants) 34(1) Mytilus—Fucus competition (Adult Plants) 37(m) Limpet marking experiment 38(n) Laboratory experimentation 39(I) Behavior experiments 39(II) Idothea selection experiments 39(III) Pagurus grazing 40(IV) Pisaster—Fucus interactions 41(V) Mytilus removal of Fucus 41DISCUSSION 42(a) Diversity and community structure 42(b) Lower intertidal distribution of Fucus 51(c) Fucus characteristics at Bowen Island and Lighthouse 53ParkSUNMARY 54LITERATURE CITED 55FIGURES 60APPENDIX 128TABLES 129ivVLIST OF FIGURESFigure Page1. Map of Bowen Island showing study area. 612. Map of Point Atkinson showing study area at Lighthouse 63Park.3. Fucus attachment to cement block. 654. Cages used in littorinid and limpet growth experiments. 675. Experimental apparatus used in laboratory experiments. 696. Frequency distribution of plant heights. 717. Frequency distribution of number of dichotomies per 73plant.8. Regression of Fucus height against number of 75dichotomies.9. Photographs of Fucus from Bowen Island. 7710. Diagram of Fucus with associated invertebrates. 7911. Changes in the number of L. sitkana over time. 8112. Changes in the number of L. scutulata over time. 8313. Changes in the number of M. edulis over time. 8514. Changes in the number of amphipods over time. 8715. Change in mean species diversity and Fucus height 89diversity over time.16. Changes in the mean number of animals on Fucus 91over time.17. Regression of species diversity against Fucus height 93diversity.18. Frequency distribution of numbers of L. sitkana. 9519. Frequency distribution of numbers. of H. plumulosa. 9720. Frequency distribution of numbers of N. edulis. 99viFigure Page21. Change in mean species diversity of the substrate 101fauna.22. Changes in mean species diversity of structurally 103different plants.23. Changes in mean species diversity for groups of 105plants.24. Changes in mean number of organisms on transplanted 107groups of plants.25. Regression of limpet length against limpet height. 10926. General pattern of Fucus zonation on Bowen Island. 11127. Pagurus—grazed Fucus. 11328. Regression of Fucus height against growing time. 11529. Growth and dichotomization of Fucus. 11730. Idothea grazing on Fucus. 11931. Changes in mean species diversity and Fucus height 121diversity.32. Frequency distribution of M. edulis. 12333. Mean growth rate of plants cleared of Mytilus and 125plants with intact Mytilus.34. Selection of Fucus by Idothea. 127viiLIST OF TABLESTable Page1. Comparison of structural characteristics of Fucus 129between Bowen Island and Lighthouse Park.2. Organisms found on Fucus and on the substrate under 130Fucus.3. Relationships between independent and dependent 131variables for Bowen Island and Lighthouse Park,seasonal data pooled.4. Relationships between independent and dependent 132variables for Bowen Island on a seasonal basis.5. Comparison of final heights of Littorina sitkana. 1346. Comparison of final heights of mature plants 135transplanted to three intertidal sites.7. Relationships between independent and dependent 136variables for Lighthouse Park on a seasonalbasis.8. Comparison of number of A. pelta remaining on 137cleared and uncleared areas.1389. Comparison of number of L. sitkana and L.scutulata found on Fucus and non—Fucus sides oflaboratory tank.10. Selection of structurally variable plants by 139Idothea wosnesenski.viiiAcknowledgementsI thank my supervisor, Dr. Ron Foreman, for his continuedsupport throughout all phases of the work leading to this thesis andfor attempting to teach me some Botany. In particular his advice,criticisms, and financial support are greatly appreciated.To Dr. Robin Harger I give a heartfelt thanks for hisconstructive comments and suggestions prior to the initiation ofthis study. Robin also critically read the original manuscript.I want to thank Susan Latimer who cheerfully assisted me inthe field and devoted some time towards preparing some of the figuresin this thesis.Thanks also to Dr. Sylvia Behrens who kindly read the originalmanuscript and to Julie Celestino who identified some of the algae.Several individuals at the Canadian Oceanographic IdentificationCentre in Ottawa assisted with invertebrate identification, in particular,J. A. Fournier, R. M. O’Clair (polychaetes), and E. L. Bousfield(amphipods).1INTRODUCTIONa) GeneralThe functional role of marine benthic algae in nearshorecommunities has been the subject of an increasing number ofinvestigations. The importance of marine algae to marine animals hasbeen recognized for some time (Scagel, 1959) but the dynamics of theinteractions between plants and animals remains largely unknown.Recent work by Mann (1972, 1973) has elucidated the significance ofbenthic macrophytes as primary producers.Few intertidal investigations have been directed at assessinginterrelationships between algal populations and associated animalassemblages. One such study (Glynn, 1965) consisted of an examinationof species interrelationships of rocky intertidal Balanus glandula—Endocladia muricata associations. Paine (1971) experimentallydetermined that mussels on a stretch of New Zealand coastline werelimited in their lower intertidal distribution through the actions of alarge brown alga, Durvillea.A number of attempts have been made to interpret associationsbetween certain terrestrial faunal communities and the structure of thepresiding vegetation. MacArthur (1965) describes a relationship betweenbird species diversity and a measure of vegetation complexity, foliageheight diversity, for North American bird populations. Over a widegeographical area bird species diversity could be predicted from knowledgeof the foliage height diversity. Pianka (1967) established correlationsbetween the structural complexity of desert vegetation, plant volume2diversity (a measure of the volume of space occupied by a particularplant) and lizard species diversity. Speculation as to which aspect ofvegetation diversity, i.e., plant structural diversity or plant speciesdiversity, is the more important in determining animal speciesdiversity has been raised (Murdoch, Evans, and Peterson, 1972) andremains unanswered.This study is, in part, an attempt to analyze the relationshipbetween the structural complexity of a common intertidal alga, Fucus,and its resident faunal assemblage. Jones (1948) examined interactionsbetween fucoids and the limpet Patella in an experimental study designedto determine the role of invertebrates in affecting intertidal algaldistributions. Jones determined that there was “... an ecologicalbalance between Patella and algae of the shore” where grazing by Patellacontrols the distribution of Fucus. The succession of algae on intertidalshores in the absence of limpets was followed by Lodge (1948) who notedan expansion of the zone occupied by Fucus vesiculosus in the absence oflimpets. The dynamic balance between limpets and Fucus has beenillustrated as a cyclic relationship (Southward, 1964) where an increasein limpet settlement can decrease fucoid populations and a decline inlimpets increases the survival rate of newly settled plants therebyincreasing the size of the overall Fucus population.The animal populations associated with Fucus have been studied,primarily in a qualitative fashion, by a few European researchers.Colman (1939) examined the invertebrate fauna of eight species of inter—tidal algae including three Fucus species, F. spiralis, F. vesiculosus,and F. serratus. In total, 177 animal species were found with copepods,3acarines and littorinids dominating in numbers. Later, Wieser (1952)investigated the microfauna of certain intertidal algal species andHagerinan (1966) quantitatively analyzed the fluctuations in animalnumbers associated with F. serratus growing sublittoraly. Experimentalmanipulative techniques were applied by Haage and Jansson (1970) whoquantified changes in animal numbers occurring in F. vesiculosus belts.Inter— and intraspecific competition among epiphytes on fronds ofF. serratus is described by Stebbing (1973).A second major aspect of this study consists of an examinationof the factors affecting the lower intertidal distribution of Fucus.Intertidal ecologists have long been concerned with identifying theimportant factors which limit the vertical distribution of both plantsand animals. Recently the importance of biological interactions indetermining the lower limits of intertidal distributions has beenreviewed (Connell, 1972). Those biological processes which are of primaryimportance have been identified from field experimentation, namelypredation (Paine, 1966, 1974; Connell, 1970) and competition (Connell,1961a, b; Harger, 1970, 1972; Dayton, 1971). The prevailing attitudestowards intertidal zonation and seaweed distributions have been examinedby Chapman (1973) who concludes that biological interactions are ofprimary importance in the lower intertidal zone. For example, competitionbetween Fucus spiralis, F vesiculosus, and F serrätus on British shoresis cited as the major process leading to distinct bands of the threespecies. I have combined field and laboratory experiments in an attemptto delineate those processes affecting the local intertidal distributionof Fucus.4b) Selected Aspects of the Biology of FucusThe genus Fucus is in the order Fucales, class Phaeophyceae.Distinguishing features of this order include discoid holdfasts, apicalgrowth via apical cells and antheridia and archegonia located onconceptacles (Fritsch, 1945). Eggs and sperm are discharged in packetsof 8 and 64 respectively with each packet enclosed by a inembranoussheath. Fertilization occurs after gametes are released from theconceptacles and the eggs are free and the sperm motile (Pollock, 1969).Laboratory studies of east coast F. distichus showed that fertilizationoccurred primarily within the conceptacle (McLachlan, Chen and Edelstein,1971). I found embryos in the conceptacles of mature plants fromBowen Island which suggests that some fertilization occurs within theconceptacle. Once fertilized the cell secretes a glue—like substancewhich acts to adhere the eggs to the substrate. Knight and Parke (1950)found that fertilized eggs of F. serratus and F. vesiculosus were widelydispersed over the shore and became firmly attached to the substratewithin a few hours. Cell differentiation occurs rapidly with a rhizoidalregion being formed at the basal pole which subsequently develops into aholdfast and a thallus region develops from a thallus cell at the apicalpole (Jaffe, 1968).Species of the genus Fucus exhibit tremendous phenotypicplasticity. The absolute number of species of Fucus remains a matterof debate but estimates range from 6 to 15 species (Powell, 1963). Dawson(1961) lists only one species of Fucus as occurring on the Pacific coastof Canada and more recent publications (Widdowson, 1973) support thistheory. This species, F. distichus, has two sub—species, edentatus and5evanescens, with both forms being found along the Pacific coast.Distinction between the forms of Fucus is often difficult in light ofthe fact that F. distichus is “... apparently most polymorphic of allon parts of the Pacific Coast of North Anterica...” (Powell, 1963).Recent investigations (Conway, 1974; personal communication), suggestthat a second species, F. spiralis, may be present on the Pacific coast.In Canada this species was formerly thought to occur only on theAtlantic coast. Pollock (1969) describes a diminutive form from theSan Juan Islands off the coast of Washington which he thought appearedsimilar to F. spiralis. The Fucus community I encountered onBowen Island appears to consist of F. distichus, a form identified asF. spiralis by Dr. Conway, and perhaps a hybrid form (Conway, 1974;personal communication). Burrows and Lodge (1951) discuss the problemof Fucus hybrids and the extent to which they occur in nature. TheFucus of Lighthouse Park is of the F. distichus type with none of the! spiralis type. Because of the taxonomic problems inherent in theclassification of Fucus I shall refer only to the genus Fucusthroughout the remainder of this thesis as it pertains to my specificinvestigation.6MATERIAL AND METHODSa) Description of Study AreasTwo major study areas were utilized for the examination ofFucus—faunal associations. The areas, Bowen Island and Lighthouse Parkon Point Atkinson, were chosen primarily because they differed in theirdegree of wave exposure. Bowen Island is situated at the mouth ofHowe Sound (Figure 1) and Point Atkinson juts into the Strait of Georgiawhere it is bordered on either side by Burrard Inlet and Howe Sound(Figure 2). The study sites of Bowen Island were situated nearGraf ton Bay (49024V N. and 124°22’ W.) and are relatively well protectedby the prominence of Gambier and Keats Islands. Point Atkinson (49°20’ N.0 , .and 124 16 W.), unlike the Bowen Island site, receives the bulk of thelarger wind generated waves from the Strait of Georgia.The intertidal zone at Lighthouse Park is characterizedprimarily by steep granite cliffs and large bouldered beaches. Salinityand temperature measurements were not made during the course of this study.Such data were obtained from published oceanographic records of theHowe Sound and Burrard Inlet area. Comprehensive oceanographic data offPoint Atkinson is not available so the values used are extracted from theoceanographic stations located closest to the study area. These arestation Burr—3 (Institute of Oceanography, U.B.C., Data Report 34, 1972;49°19.l’ N. and 123°12.1’ W.) and station 15 (Waldichuk, Markert, andMeikle, 1968; 49°19.30’ N. and 123°17.50’ W.). Salinity values rangedfrom a low of liZa to a high of 23%. over a ten year period from 1962 to1972. Temperature variation for the same period of time ranged from about76°C to 18.5°C.The shorelines on Bowen Island range from steep cliffs togently sloping sandy and pebble beaches. The main study area consistedof large and small bouldered beaches interspersed with large rockoutcrops. The closest oceanographic stations to the study area wereHow—2 and How—2.5 (Institute of Oceanography, U.B.C., Data Reports 30and 34; 49°23.3’ N. and 123°l7.8’ W. (How—2) and 49°27.O’ N. and123°16.0’ W. (How—2.5)). Data from station 11—12 (Waldichuk, Markert,and Meikle, 1968; 49°25.20’ N. and 123°26.27’ W.) were also considered.Temperature values between 1962 and 1972 ranged from 6.3°C and 18.7°C.Salinity values ranged from 12.35%. to 22.49%.. over the same time period.The two study areas, notwithstanding the paucity of oceanographic data,seem to be influenced by similar temperature and salinity regimes.Fucus is the numerically dominant intertidal alga at BowenIsland in terms of numbers of individual plants, biomass, and areacovered. The upper limits of Fucus coincide with the maximum upperlimits of Balanus glandula in most areas. Rhodomela larix can be foundin adjacent tidepools and small crevices, and Prionitis lanceolata iscommon in the few small tidepools of the area. Some Spongomorpha sp. andEnteromorpha sp. also occur in scattered patches at certain times of theyear.At Lighthouse Park, Fucus also tends to be the dominant algain terms of abundance but the presence of many tidepools provides a habitatfor a variety of other forms. Laminaria saccharina and Alaria sp. arequite common on rocks in the lower intertidal zone and in tidepools higher8in the intertidal region. Other forms found during the investigationare Microcladia coulteri, Prionitis lanceolata, Iridaea cordata andspecies of Enteromorpha, Ulva, Monostroma, Pylaieila, Rhodoglossum andPorphyra. The epiphyte, Elachistea fucicola, frequently grows on Fucus.b) Data Analysis MethodsThe measurement of the diversity of an assemblage oforganisms ranges from simple enumeration of the species present in acollection to the indices based on information theory (Shannon, 1948).The index based on information theory, (H’), is a measure of theuncertainty of identification of an individual picked from a collectionof individuals where,=1:1log 1= proportion of individual organismsrepresented by the th species.s = total number of species.A second index (B) (Brillouin, 1962) measures the informationcontent of a total collection of organisms where,B = 1og2,N2’ NJj bits of informationN = total number of organismsN1 = number of organisms of species 1N2 = number of organisms of species 2N = number of organisms of species s9The diversity per individual (H) Pielou, 1966) is obtained bydividing the expression for (B) by the total sample size:H = ‘ log, N2!...Ni1The index (H’), unlike (H), is not dependent on sample size and is usedwhen the sample being analyzed contains all the species present in theparent population (Pielou, 1966). Harger and Tustin (1973a) point outthat much confusion remains in the literature over the usage of (H’) and(H), and that both indices should be reported together to aid incomparisons with other investigations. The application of diversitymeasures as interpretive tools in the analysis of community structurehas been questioned. Hurlbert (1971) suggests that species diversityhas become a “meaningless concept” but his desire to abandon the conceptof species diversity has been labelled “premature” by Hill (1973) andHarger and Tustin (1973b) suggest that Huribert’s species abundanceratios in lieu of diversity measures will not complement present understanding of community structure and function. In this study both speciesdiversity (H’) and diversity per individual (H) have been presentedtogether.Measurement of diversity is not restricted to speciescomposition but can be equally applied to other characteristics ofcommunities and populations such as species biomass, height distributionsetc. I have applied information theory in analyzing the heights ofindividual Fucus plants to obtain a measure of Fucus height diversity.Each plant was assigned a size class and classes were defined at 3 cmintervals. For example, all plants 0—3 cm in height are in the first10category, those 3—6 cm in height are in the second category, and so on.The information formula (H’), is applied to the proportion of plants ineach category to obtain the measure of Fucus height diversity.c) Bowen Island Sampling TechniquesAn intertidal sampling program was initiated in May, 1973and continued through July, 1974. Vertical Line transects extending fromthe uppermost limit of the Fucus zone to the lowest intertidal limit wereutilized. Sampling was performed using a 0.1 m2 quadrat at approximately1 meter intervals down the transect. Two somewhat different Fucussampling techniques were employed. In one method the percentage of thequadrat covered with Fucus was estimated visually and expressed as apercentage cover value. Individual plants within the quadrat were removedsingly from the substrate by means of either a sharpened putty knife orwith the use of forceps. Each plant was searched for its associatedorganisms and if any were found the distance each organism was situatedfrom the plant holdfast was measured with a centimeter ruler. Followingsuch measurements each plant along with those organisms found on it wasplaced in a labelled plastic bag. Those plants on which no organisms werefound were placed collectively in a separate labelled bag. The portionof those plants overlapping the quadrat from outside was also collected.After all plants from the quadrat had been removed in this manner, theinvertebrate fauna associated with the rock substrate within the quadratwas collected. The slope of the substrate was then visually estimated(e.g., 400) and also the type of substrate (e.g., pebble, boulder, etc.).The second sampling method utilized was essentially similar to11the first except that the position of the animals on each plant wasnot determined; rather, all plants and their associated fauna weresampled collectively. In this way a more rapid estimate of populationabundance could be determined.All samples collected were sorted in the laboratory. Thefauna of each individual plant was counted and recorded. The maximumheight of each plant was obtained using a centimeter ruler. A secondmeasurement, the total number of dichotomies which resulted in frondsgreater than one centimeter in length, was determined for each plant.This measure arose from a need to have a comparable measure ofindividual plant complexity which could be used in assessing structuraldifferences between plants from different areas. Also it was thoughtthat such a measure would be a biologically important factor that couldbe related to animal community structure. The wet weight of the Fucusin each quadrat was determined once all the animals were removed. Theplants were then dried in a drying oven at 105°C for 36 hours to assessdry weight. For each quadrat the following measurements were recorded,each of which became an independent variable in the multiple regressionanalysis which is discussed later.1. Total number of plants.2. Total cumulative height of all plants.3. Total number of dichotomies.4. Mean height per plant.5. Mean number of dichotomies per plant.6. Ratio of total number of dichotomies to total height.7. Wet weight of Fucus.128. Dry weight of Fucus.9. Cover value (%).10. Distance along intertidal transect.11. Fucus height diversity.d) Fucus Transplantation ExperimentsExperimental manipulation of intertidal algae is a difficulttask. Descriptions of methods used are sparse for most intertidal formsexcept for techniques utilizing the transplantation of algal coveredboulders to various parts of the intertidal zone (Pollock, 1969) and thetransplantation of large kelps such as Macrocystis (North, 1964; Pace,1972) in the subtidal zone. Waaland (1973) developed a simple techniqueusing polyethylene clamps to transplant species of Iridaea and Gigartinato different depths in growth experiments. A new technique for thepresent experimental program which involved transplantation of individualFucus plants onto replicate cement blocks was devised. Considerable timewas spent in experimenting with a variety of possible techniques prior tochoosing the method used which is as follows: An electric drill with a¼ inch drill bit was used to drill a 2 inch deep hole into a cement block.Experimental plants were scraped from the substrate with their holdfastsintact. A ½ inch long piece of vinyl plastic tubing (I.D. one—eighth inch;O.D. ¼ inch) was slit lengthwise. The stipe of the plant was placedthrough the slit in the tubing with the holdfast extending from one endand the fronds of the plant, the other. Using forceps, the holdfast—tubingcomplex was pressed into the hole in the cement block until the top of thetubing was flush with the surface of the cement block (Figure 3). Thistechnique proved to be satisfactory for about a 4 to 5 month period. Plants13were lost after this time, apparently due to a hardening of the plastictubing and the subsequent loss of the tubing’s inherent resiliency.e) Transplantation of Structurally Variable PlantsCement blocks (20.0 cm x 9.5 cm x 5.5 cm) were drilled with asingle hole in the center of the block. A single plant was thenattached to each block in the previously described method. Three levelsof plant complexity were used with each level differing in the numberof dichotomies per plant. All plants were approximately 20 cm in heightand had either 30 or more dichotomies (high complexity), 20 dichotomies(medium complexity), or less than 10 dichotomies (low complexity). Threeblocks of each complexity level were then transplanted to each of threeintertidal sites in May, 1973. The three sites were arbitrarily chosenas being an area of either high Fucus density (cover value greater than90% per 0.1 m2 quadrat), medium Fucus density, or low Fucus density.Faunal colonization of the transplanted plants and the cement blocks wasrecorded over the experimental time period which extended to September,1973. Three control blocks with no plants attached were also placed ineach of the three sites.f) Fucus Density EffectsCement blocks (23.0 cm x 15.0 cm x 8.0 cm) were drilled with20, 15, 10 or 5 holes with all holes clumped in the center of the block.Fucus plants of approximately the same height and with the same numberof dichotomies were obtained in the manner described previously andattached one per hole to the experimental blocks. Three of each type14of block—plant complex were placed in each of two areas, a high densityFucus area and a low density Fucus area. The transplanted plants wereexamined periodically for the presence of invertebrates over a period often weeks.g) Littorinid and Limpet Growth ExperimentsAn attempt was made to determine the effects of structurallydifferent Fucus plants on the growth of two intertidal invertebratescommonly associated with Fucus; Ljttorina sitkana and Acmaea pelta.Stainless steel framed cages (15.0 cm x 10.0 cm x 10.0 cm) were enclosedin a nylon mesh bag (mesh diameter 3.0 mm) and attached to 23.0 cm x15.0 cm x 8.0 cm cement blocks with stainless steel anchor bolts (Figure4). Provision was made for attachment of a single plant per cage. Theexperimental design consisted of cages containing either no Fucus, aplant trimmed to less than 10 dichotomies, or a plant with greater than25 dichotomies. Three cages of each design containing 10 Littorinasitkana were placed in each of three intertidal areas: a low, medium, andhigh density Fucus area. Prior to being placed in the cages each animalwas marked with orange cellulose base paint and the height of each animaldetermined with vernier calipers.In a different set of cages 7 Acmaea pelta each were placed.Each cage contained either no Fucus, a plant trimmed to less than 10dichotomies or a plant with greater than 25 dichotomies. The length andheight of each animal was measured with vernier calipers prior to beingplaced in the cages. Three cages of each experimental design were thenplaced in each of a low, medium, and high density Fucus zone along with15the littorinid cages. After a period of 18 weeks all animals wereremoved from the cages and measured. The possible loss of cages from logdamage at this time made it unfeasible to continue the experiment.h) Fucus Growth MeasurementsTo gain some insight into growth rates of mature and juvenilefucoids, experimental manipulative techniques were employed along within situ tagging of specific plants. Fifteen plants greater than 10 cm inheight were attached singly to cement bricks (23.0 cm x 15.0 cm x 8.0 cm)and placed in each of three zones; a high intertidal zone correspondingwith the upper limits of Fucus, a mid intertidal zone corresponding tothe area of maximum numbers of Fucus plants, and a low intertidal zonewhich was below the lower limits of any naturally occurring large fucoids.Growth and dichotomization of these plants was measured over time.Five juvenile plants were selected from each of the above threeintertidal sites and left intact on their natural substrate. Theseplants were tagged with orange colored surveying tape tied loosely abovethe holdfast and their position mapped to aid in their subsequent location.The growth of the plants was recorded over time.h) Investigations of Factors Affecting the Lower Intertidal Limits ofFucus(I) Pisaster—mediated mortalityAn hypothesis was formulated to determine the effect ofPisaster ochraceus predation on Balanus glandulain the lower intertidalzone as a factor which acts to indirectly control the lower intertidal16distribution of Fucus. To test this hypothesis, 10 large rockscontaining Fucus which was attached to Balanus glandula growing on therocks, were transplanted into an area of high Pisaster activity.Similarly, 10 equally sized rocks containing Fucus which was attacheddirectly to the rock surface were transplanted to the Pisaster area.All rocks were regularly monitored for the removal of Fucus.A second test of the Pisaster—induced mortality hypothesisconsisted of placing 6 rocks with 103 Fucus plants attached to Balanusglandula and 4 rocks with 70 Fucus plants attached directly to the rocksurface into a large plastic meshed bag (vexar, mesh size 3.5 mm)along with 5 Pisaster. The bag was sewn shut with nylon cord and placedin the intertidal zone in the area of Pisaster activity. The number offucoids remaining on the rocks was determined after 4 weeks.(II) Hermit Crab GrazingDuring the course of this investigation field observations ledto a hypothesis of hermit crab grazing causing heavy mortality of juvenileFucus growing low in the intertidal zone. To test this hypothesis rockscontaining 71 small fucoids were placed in the low intertidal zone alongwith rocks containing 25 juvenile plants which were enclosed in vexar bags.The numbers of plants and the condition of the plants remaining at the endof the experiment in August, 1973 was recorded. Also two rocks with Fucuswere enclosed in a vexar bag and placed with two non—enclosed rocks ineach of two small tidepools where there was an abundance of hermit crabsand an absence of fucoids. The rocks were checked periodically for signsof grazing.17(III) Balanus—Fucus CompetitionPossible competitive interactions between Balanus glandulaand juvenile Fucus were examined by the removal of any B. glandula whichtouched a selected group of 15 Fucus holdfasts. A control group of 15plants was left with surrounding B. glandula intact. Both sets of plantswere mapped and their survival watched over time.j) Lighthouse Park Sampling TechniquesSampling techniques used at Lighthouse Park were identical tothose used at Bowen Island. An attempt to duplicate the Fucus transplantexperiments of Bowen Island failed at Lighthouse Park because of thehigh wave—induced mortality of the transplanted plants. As a resultexperimentation at Lighthouse Park was limited to the examination ofspecific faunal—Fucus interrelationships.k) Mytilus edulis—Fucus CompetitionObservations of dense accumulations of the mussel Mytilus edulisadjacent the lower edge of the Fucus zone resulted in an experiment totest the possible effects of M. edulis on the growth and survival of Fucus.Dense accumulations of Mytilus which grew around the base of and directlyattached to juvenile Fucus plants were removed from 4 groups of six plantswhich were subsequently kept free of Mytilus with each visit to theexperimental site. Similar numbers of control plants were left withtheir Mytilus complement intact. The growth and survival of control andcleared plants was recorded for the duration of the study.In a similar experiment, all Mytilus were removed from 1018mature (greater than 15 cm in height) plants while a control group of10 plants was left with their associated Mytilus intact. Growth andsurvival of these plants was also monitored for approximately 2.5 months.1) Limpet Marking ExperimentsRepeated qualitative examinations of Fucus—inhabited zones atLighthouse Park led to observations of many limpets, primarily Acmaeapelta, being found under the fronds of Fucus. Such observations led toan experiment to determine if this association was merely coincidental or,rather, if the limpets were choosing under—Fucus habitats. The firstexperiment commenced in May, 1973. Two adjacent areas, each about 2 m2,were chosen each of which contained a dense cover of Fucus and manyA. pelta. All the Fucus was removed from one of these areas and leftintact in the other. The liiupets in the cleared area (n43) were markedwith red paint and all limpets in the intact area (n=60) were marked withorange paint. The two areas were checked periodically for the presenceof marked limpets. The experiment was duplicated a second and third timewith some slight modifications. Two smaller adjacent areas eachapproximately 0.25 m2 were demarcated, one cleared of all Fucus, the otherleft in its natural state. Twenty liinpets from a nearby site were obtainedand marked, 10 red and 10 orange. Ten limpets were placed in the clearedarea and 10 in the uncleared area. Each limpet was wetted with seawaterand observed until it was firmly attached to the substrate. Each area waschecked for marked limpets with each trip to the experimental site.19m) Laboratory ExperimentsLaboratory experiments commenced in the summer of 1973 in aseawater equipped lab at the Vancouver Public Aquarium. Theexperiments were designed to duplicate some of the field experiments andto investigate specific interactions between certain invertebrates andFucus.(I) Littorina and Acmaea Behavior ExperimentsThe ability of Littorina sitkana, L. scutulata and Acmaea peltato detect the presence of Fucus and react to its presence was testedusing the apparatus shown in Figure 5. The apparatus consisted of aplexiglass flow tray with two separate holding compartments, one of whichheld some Fucus and the other left empty. Seawater flowed into eachcompartment and over the bottom of the tray where the experimental animalswere situated. A 10 cm long plexiglass plate served to separate the twostreams of discharged water. Carmine particles were used initially toensure that stratification of the two streams did occur on the bottom ofthe tray. A drain hole was situated at each end of the tray through whichthe discharged water flowed. Fifty L. sitkana or L. scutulata were placedin the center of the tray and the entire complex was covered with blackplastic sheeting to remove any source of light which could influence theanimal’s behavior. The animals were left for 24 hours after which timetheir position in the apparatus was noted. The experiment was repeatedusing a complement of 10 Acmaea pelta.20(Ir) Idothea Selection ExperimentsThis experiment was designed to determine if certain motilespecies which were found with Fucus, visually selected plants of aspecific structural morphology. The isopod, Idothea wosnesenski, andamphipod, 1-lyale plumulosa, were selected for the experiment but problemsin working with the small amphipods led to my using only Idothea.Four levels of plant complexity were selected for use in the experimentas follows:Level 1 Plants with more than 40 dichotomiesLevel 2 Plants with 20 dichotomiesLevel 3 Plants with 10 dichotomiesLevel 4 Plants with 0—5 dichotomiesOne plant of each level was anchored in the corner of a 10 gallonaquarium tank so that the blades floated freely in the water column. Inthe first series of experiments, 10 Idothea were placed in a small, open,weighted beaker in the center of the tank and left for 18—24 hours duringwhich time the animals were free to migrate about the tank. The sides ofthe tank were blacked out to allow only surface light to enter the tank.After the time period each plant was removed and the number of Idotheafound on each plant recorded. The experiment was repeated with thearrangement of the plants in the tank changed with each new experimentaltrial. Complements of 15 and 25 Idothea were used in subsequentexperiments.(III) Pagurus Grazing ExperimentThis experiment was designed to determine it hermit cz’abs21utilized Fucus as a food source as suggested from field observations.Twenty hermit crabs collected from Bowen Island were placed in a 10gallon tank with a rock containing 30 small fucoids and a rock with 45fucoids enclosed in a vexar bag. Food material in the form of crushedMytilus and Balanus was added periodically to the tank in an attemptto duplicate the “normal” conditions under which the hermit crab isnaturally found. The plants were examined daily for signs of grazingand the behavior of the crabs was observed during the course of theexperiment.(IV) Pisaster—Fucus InteractionsThis experiment was also a duplication of a similar fieldexperiment. Rocks containing 54 Fucus attached to Balanus glandula wereplaced in a 15 gallon tank along with rocks containing 50 plants whichwere attached directly to the rock surface. Four Pisaster ochraceuswere added to the tank. The survival of all plants and the behavior ofthe starfish was recorded over time.(v) Detachment of Fucus by MytilusAn observation of adult plants growing in clumps of Mytiluswith their holdfasts detached from the substrate led to a laboratoryexperiment to determine if M. edulis was responsible for removing theplants from their substrate. A rock with 70 fucoids of various heightswas enclosed with 200 Mytilus in a vexar bag and left in a 10 gallonaquarium tank for 2 months. After this time the Mytilus were carefullyremoved from the rock and the number of plants which remained firmlyattached to the substrate noted.22RESULTSa) Bowen Island and Lighthouse Park Fucus Population CharacteristicsDuring the course of this study over 5,000 plants from the twostudy areas were measured for total length and degree of dichotomization.The number of dichotomies per plant and the total height of plantsdiffered between the two sites. The comparisons were based on 100 plantseach, chosen randomly from each site. At Bowen Island, 51% of the plantswere 0—3 cm high, 24% between 3—6 cm high and 11% between 6—9 cm high.The remaining 14% were between 9—18 cm hEgh (Figure 6—A). At LighthousePark 18% of the plants were between 0—3 cm, 18% between 3—6 cm, 21%between 6—9 cm, 16% between 9—12 cm, 18% between 12—15 cm, 6% between15—18 cm, and 3% were greater than 18 cm (Figure 6—B). The individualplants at Lighthouse Park tended to be taller than those of Bowen Island.The degree of dichotomization also differed between the two areas.Plants at Lighthouse Park tended to have more dichotomies than those atBowen Island (Figure 7). Of the 100 randomly selected plants 83% of thosefrom Bowen Island had between 0—5 dichotomies, while only 54% of the plantsfrom Lighthouse Park had between 0—5 dichotomies.The relationship between plant height and the. respective numberof dichotomies for each area is displayed as regressions in Figure 8.Comparisons of the regression lines indicates that the degree ofdichotomization is greater at Lighthouse Park. Other plant characteristics compared between the two study areas were the number of plants perquadrat, the mean height of plants per quadrat, and the number ofdichotomies per plant. Table 1 shows the analysis of variance results of23these comparisons. No significant difference in number of plants perquadrat or the number of dichotomies per plant was revealed but the meanheight of plants at Lighthouse Park was significantly greater than atBowen Island.Periods when plants were reproductive varied within the studyareas. On Bowen Island an upper intertidal form (Figure 9—A) attainedmaximum development of conceptacles in winter and continued through earlysummer. A lower intertidal form began to mature reproductively in Juneand was apparent in a reproductive state through October (Figure 9—B).Recruitment of Fucus could potentially occur the year round on BowenIsland. At Lighthouse Park, reproductive maturity as indicated by fullydeveloped conceptacles was maximal in the spring and summer months.b) Bowen Island SamplingVertical intertidal transects on Bowen Island revealed spatialand temporal patterns in the abundance and diversity of organismsassociated with Fucus. A variety of organisms occur associated with thealga in one of the following fashions:Degree of Association Example1) Directly attached Balanus glandula, Mytilus edulis2) Slow moving, clinging forms Acmaea pelta, Littorina sitkana3) Active clinging forms Idothea wosnesenski4) Forms associated with algal Hyale plumulosaexudate or water entrainedby the plant5) Migrant forms which enter Cottid fishesFucus habitats at high tide24The total complement of species found in association withFucus throughout the study period is illustrated in Table 2. Adiagrammatic representation of some of the dominant invertebratescomprising the Fucus fauna is shown in Figure 10. Seasonal trends inthe abundance of the dominant organisms, Littorina sitkana, L. scutulata,Mytilus edulis, and Hyale plumulosa are illustrated graphically inFigures 11 to 14. The amphipod, Hyale plumulosa, displayed the greatestvariation in numbers on seasonal basis. Very low numbers (less than 10per 0.1 m2 quadrat) could be found in the spring of 1973 and winter ofl97344 while maximum numbers were found in the summer months of both1973 and 1974. The numbers of Littorina sitkana also demonstrated clearseasonal fluctuations with a minimum number present in January, 1974, andpeaks in population abundance during the spring and summer of 1973 and 1974.Little seasonal variation was evident in the numbers of Littorina scutulataand Mytilus edulis except for a decrease in abundance during winter. Thenumbers of L. scutulata were seldom greater than 20 per 0.1 m2 quadrat(Figure 12—A) and the numbers of N. edulis were usually below 25 perquadrat (Figure 13—A).Seasonal variation in species diversity of the assemblage oforganisms associated with Fucus was evident. Figure 15 illustrateS theseasonal variability in species diversity (H’). Peaks in mean (H’)appeared in May 1973, August 1973, and July—August 1974. Periods of lowdiversity occurred in July 1973 and a decline in diversity was evident inthe winter months of 1973—74.Stepwise multiple regression analysis (UBC BND:02R) was employedto compare the variation in species diversity (H’), diversity per25individual (H), and numbers of organisms found on Fucus with theindependent variables listed on page 11. When all the seasonal dataare pooled, no definite trend emerges from the analysis (Table 3).For species diversity (H’) the total number of dichotomies accountedfor 16.41% of the variation in (H’) with the intertidal quadrat positionaccounting for 5.80% of the variation and the mean height of plants,3.36% of the variation. For diversity per individual, (H), the numberof dichotomies accounted for 21.02% of the variation with distancealong the intertidal transect and the mean height of plants accountingfor 6.38% and 3.93% of the variation respectively. The total cumulativeheight of all plants pert quadrat was responsible for a 4.24% reductionof the variation in numbers of organisms with the number of plantsaccounting for 3.71% and quadrat position along the intertidal transect1.76%. The seasonal variation in mean numbers of organisms per quadratis illustrated in Figure 16. Separating the data into respective seasonalcategories yielded results which indicate that different factors areattributable for most of the variability in species diversity and numbersof organisms found associated with Fucus at different times of the year(Table 4). In January, 1974, Fucus height diversity accounted for thegreatest reduction in species diversity (H’). The position of the quadratalong the intertidal transect was responsible for 31.40% of the variationin (H’) during April—May and 14.06% of the variation in August. In Julyand in the September—October time period reduction of the variation in (H’)was closely associated with plant structural characteristics such as meannumber of dichotomies (July) and mean plant height (September—October).The seasonal variation in Fucus height diversity is shown in26Figure 15 along with the variation in species diversity (H’).Synchronous fluctuations are apparent between the two indices with theclosest correlations between (H’) and Fucus height diversity occurringwhen both values are at their seasonal minimum (July, 1973; January,1974). Regression analysis comparing the relationship between Fucusheight diversity and species diversity resulted in a significantcorrelation between the two variables (Figure 17).The distributions of the dominant organisms on individualplants are shown as frequency distributions of numbers of organismsagainst distance along the plant from the plant holdfast. The numbersof Littorina sitkana on plants of five size ranges (0—5 cm, 5—10 cm,10—15 cm, 15—20 cm, and greater than 20 cm) are shown in Figure 18. Asthe size range of the plants increases, the distribution of L. sitkanaon the plants shifts with peaks in abundance shifting from a position onthe lower 0—1 cm of the plant (adjacent to the holdfast) for plants 5 cmor less, to a peak over 20 cm from the holdfast on plants greater than20 cm in height. The amphipod distribution, Figure 19, does not followany specific pattern. On shorter plants the amphipods tend to be clumpednear the holdfast while on taller plants no clear pattern of amphipoddistribution is evident. The distribution of Mytilus edulis is skewedfor plants 0—10 cm in height with the distribution becoming moredispersed on plants greater than 10 cm (Figure 20).The species diversity of the organisms on the substrate withinthe quadrats showed little seasonal variation relative to the diversityof the fauna associated with Fucus except for a peak in May, 1973. Alist of those organisms found on the substrate under the Fucus canopy is27shown in Table 2. Multiple regression analysis indicated that Fucusheight diversity accounted for most of the variation in substrate speciesdiversity (H’) and diversity per individual (H) which was only 6.98%and 6.80% respectively. The total cumulative height of the plants perquadrat accounted for 9.82% of the variability in numbers of organismsper quadrat. Figure 21 displays the change in mean substrate diversity(H’) over time.c) Fucus Transplantation ResultsOver the 12 week period during which active colonization of thetransplanted Fucus plants occurred the species diversity of thecolonizing community varied considerably. Figure 22—A shows the weeklyvariation in mean species diversity (H’) for the three plant complexitytypes transplanted into a low Fucus density area. Variations in diversitywith each plant type were quite synchronous except for the diversity onmedium complex plants which peaked after five weeks to a level far greaterthan that of the other two plant types. A drastic decline followed thispeak with diversity levels again becoming synchronous with the otherplant levels. Plants of the lowest level of complexity were the last tobe colonized (3 weeks) and were virtually free of organisms following thethe 12 week experimental period. The plants of the highest level ofcomplexity generally maintained a more diverse community of organisms.The dominant organisms for the transplanted plants were Littorina sitkana,L. scutulata, Hyale plumulosa, Mytilus edulis, and Idothea wQsnesenskiwith littorinids being the first species to be found on the transplantedplants.28Those plants transplanted into a zone of medium Fucusdensity also exhibited fluctuations in species diversity (H’)(Figure 22—B). Colonization of these plants was somewhat slower thanof the plants in the low density Fucus area. No clear trends emergedexcept for a peak in diversity around the eighth week followed by adecline on the low and high complexity plants with an increase indiversity to the twelfth week.For those plants of the high density zone, synchronousfluctuations were again evident with increases and decreases in diversityover time. Colonization occurred after one week on the low and highlevel of complexity plants, but significant colonization of mediumcomplex plants did not occur until between the fifth and eighth week(Figure 22—C). Figure 22—D shows all three categories of plants combinedover all three density areas. The greatest fluctuations are evident onthe highest complexity plants. After eight weeks species diversity (H’)was maximum for the high and medium complexity plants unlike the lowlevel plants which tended to increase in a series of steps up to thetwelfth week.d) Density TransplantsThe results of investigations of the effect of plant density onthe diversity of the colonizing population were hampered somewhat byheavy losses of the transplanted plants. The experiment had to beconcluded after 10 weeks because of these losses. Figure 23—A shows thechange in mean species diversity (H’) over time in the low density Fucusarea. For those blocks containing 0—10 plants, species diversity wasmaintained at a low level (less than 0.75) throughout the experimental29period. For blocks with more than 10 plants, plant losses haltedanalysis after the second sampling period. In the zone of high densityFucus, mean (H’) was generally higher (greater than 1.15) than valuesobtained in the low density Fucus zone (Figure 23—B). Diversity of theassemblage of organisms on Fucus peaked after five weeks for both highand low density blocks. The high density blocks maintained a slightlymore diverse, although not significantly greater, community than lowdensity blocks. It is interesting to note that the time of the peakdiversity (5 weeks) coincides with the time of maximum species diversityobtained in the intertidal sampling program, e.g., August, 1973.Figure 23—C displays the mean (H’) over time for both the high and lowdensity areas combined.The initial colonizers in both high and low density Fucus areaswere Littorina sitkana and L. scutulata. The numbers of L. sitkana andL. scutulata increased over about a five week period when substantialnumbers of the amphipod, Hyale plumulosa were noticed. Idothea was presentafter 5 weeks and Mytilus began to attach to overhanging fronds afterabout 8 weeks. At the end of the 10 weeks, L. sitkana and L. scutulataagain numerically dominated the Fucus faunal community and the numbers ofHyale and Idothea had declined. Figure 24 shows the change in mean numbersof organisms over time for both high and low density Fucus areas. For bothareas the mean numbers of organisms found on low density blocks weresimilar and at no time were more than 50 individual organisms present. Inboth areas the numbers of organisms declined towards the end of theexperiment. Results for the high density blocks are unfortunatelyincomplete yet they illustrate a trend of a rapid increase in organisms30to a maximum number of 146 in the low density Fucus area and 192 in thehigh density Fucus area followed by a marked decline in both areas.e) Littorina and Acmaea Growth ExperimentsSignificant differences in limpet growth rates between thethree treatments (no Fucus, medium complexity Fucus, and high complexityFucus) were not evident. The loss of paint marks on some individualanimals and the mortality suffered by others rendered impossible validstatistical comparisons. Length—height regressions of the initial andfinal animal sizes for each treatment are presented, however, forillustrative purposes (Figure 25).Growth rates of Littorina sitkana were similar for alltreatments. Analysis of variance comparisons (Table 5) of the finalsizes of the animals for each treatment resulted in an insignificantF—value (F=0.232, p=O.O5).f) Factors Affecting the Lower Intertidal Limits of FucusSubjective observations of the intertidal region reveal azone of Fucus with very distinct lower intertidal boundaries (Figure 26).The distinctive nature of the distribution of mature plants coupled withobservations of juvenile plants and clumps of mature plants growing belowthis marked boundary suggested that a biological rather than a physicalinfluence was determining the lower distributional limits of Fucus. Thepresence of Pisaster ochraceus located up to the lower level of Fucus andthe obvious destruction of Balanus glandula and Mytilus edulis throughPisaster predation below the Fucus zone indicated that the predatory action31of ?isaster in the low intertidal zone was indirectly causing heavymortality of Fucus by destroying the barnacles to which the fucoids wereattached. The placement of rocks containing Fucus plants which wereattached to Balanus glandüla proved to be an unsuccessful test of thePisaster—induced mortality hypothesis. This, I believe, is the resultof the seasonal migration patterns illicited by Pisaster. In May, whenthe experiment was initiated, Pisaster was evident in the mid—intertidalregion. However, Pisaster rapidly disappeared from this area by mid Maypresumably from migration and not predation, and were not evident untillate August, 1973. Diving observations during the summer revealed largeaggregatipns of Pisaster in the subtidal zone.The second test of the hypothesis was successful. Of the 103plants attached to Balanus glandula on rocks placed in the vexar bag only31 remained after 4 weeks representing a mortality of 62.1%. Of anoriginal total of 70 plants attached directly to the rock surface, 64remained after 4 weeks with a mortality of only 9.3%. Those plants whichwere originally attached to barnacles were found in the bag, theirholdfasts still attached to a barnacle plate. Those plants remaining onthe rocks were attached to intact barnacles that had not been eaten byPisaster or were directly attached, to the rock surface. This experimentwas duplicated under laboratory conditions where similar results wereobtained (discussed later).g) Hermit Crab GrazingDefinite signs of what appeared to be hervivore grazing onplants in the lower intertidal zone was noticed in early August, 1973.32Prior to this time no visible indication of grazing was noticed onjuvenile plants growing in the low intertidal zone. Typically, grazedplants differed from ungrazed plants in having serrated edges (Figure 27).Of 71 juvenile fucoids (less than 3.0 cm in height) transplanted to thelow intertidal zone at the beginning of August, 1973, a total of 30remained on August 26, representing a mortality of 43.3%. All thesurviving plants were extensively grazed. The 25 plants which wereenclosed in a vexar cage were all present after the above time periodwith no visible signs of grazing. Similar results were obtained withcaged and. uncaged plants which were placed in tidepools.Hermit crabs could often be found situated on the tips of theplants in tidepools engaged in what appeared to be grazing activity.Groups of plants placed in the low intertidal zone in June, 1974 remainedstructurally intact until August when grazing by Pagurus began again.h) Balanus-Fucus CompetitionThe examination of possible competitive interactions betweenBalanus glandula and Fucus yielded no definite conclusions. The mortalityof all plants, treatment and control, was too high for valid comparisonsbetween the two groups of plants. No significant reduction in Fucusmortality occurred as a result of removing those barnacles whichencroached upon Fucus holdfasts.i) Plant Growth StudiesGrowth studies of tagged plants from the high and mid intertidal areas are displayed in Figure 28. The mean height of plants at thestart of the experiment (June, 1973) in the upper intertidal zone was332.62 cm. At the conclusion of the growth period in October the meanheight was 7.47 cm representing a total mean growth rate of 4.84 cmover a five month period.The mean height of plants in the mid—intertidal zone at theinitiation of the experiment was 2.05 cm with a final mean height of8.67 cm representing a growth rate of 6.62 cm over the 5 month growthperiod. These rates indicate a trend of more favorable growth in themid—intertidal areas.Juvenile plants were also tagged in the low intertidal zonefor measurement of growth rates but mortality of these plants was toohigh to allow for meaningful comparisons with other tidal levels.In January, 1974 a new settlement of Fucus appeared on some ofthe cement blocks that had been left over winter. The mean height of10 randomly selected plants at this time was 0.029 cm. The density ofplants on the blocks averaged 173 plants/lOO cm2 (mean of 5 quadrats).The growth rates and increase in dichotomization were followed untilSeptember, 1974, and are depicted in Figure 29. The rate of growthwas rapid, growing a mean of 14.8 cm from January to September.Dichotomies greater than 1 cm in length did not appear until June whenthe plants were approximately 7—8 cm in height. After this time dichotomization increased from a mean of 4.8 to 28.2 in September. The densityof plants declined considerably over the 9 month study period, with thefinal mean density in September only 27 plants /100 cm2. The actualmechanisms of the thinning process are unknown although it seems probablethat Idothea predation resulted in the death of many plants. InApril, 1974, a population of isopods (Idothea wosnesenski) colonized the34Fucus plants on the cement blocks and persisted until September.Grazing marks from Idothea (Figure 30) and Pagurus on smaller plantswere quite evident. The grazing marks left by Idothea differ from thoseof Pagurus in being much larger and lack the serrations incurred on theplant by Pagurus. An assemblage of L. sitkana, L. scutulata, Hyale plumulosaand occasionally Pagurus became associated with the plants over thesampling period.The mortality of large transplanted plants was high,especially for those plants transplanted into, the low intertidal zone.Analysis of variance comparing growth rates after three months indicatedno significant differences in growth rates between the three areas(Table 6). Extensive grazing and loss of fronds from the low intertidalplants prevented comparisons of rates of dichotomization between the threeareas.j) Lighthouse Park SamplingThe faunal community associated with Fucus at Lighthouse Parkwas less diverse than the Bowen Island fauna. A single species,Mytilus edulis, tended to dominate the community and often, as isdiscussed later, played an important role in controlling the intertidaldistribution of Fucus and, perhaps, the morphology of the plants.Acmaea pelta, Littorina scutulata and L. sitkana comprised the remainingnumerically dominant forms but these species, relative to Bowen Island,were few in numbers. Figure 31 shows the seasonal fluctuations in meanspecies ciiversity (H’) with an initial low in early May, 1973, (H’=0.l73)followed by seasonal maximum (H’=l.043) in mid May with a secondary low of350.529 in July, 1973. From August to April, 1974 no dramatic increaseor decrease in diversity was apparent although sampling was not carriedout during the winter months because of the difficulty involved withworking in the area at night. A plot of seasonal changes in mean numbersof individuals reveals fluctuations with the peaks in abundance being inMay and August, 1973 (Figure 16). Table 2 gives a species list of thoseorganisms found associated with Fucus at Lighthouse Park. Changes in thenumbers of dominant organisms are shown in Figure 11—14. Levels ofLittorina sitkana and L. scutulata abundance were characteristically lowexcept for a peak of 15 L. scutulatain mid May, 1973. High levels ofMytilus edulis were found throughout the sampling period with the maximumnumber obtained per quadrat being 800 early in May, 1973. Aiuphipods,Hyale plumulosa, were seldom found except during the summer months whenthey peaked in abundance. Fucus height diversity fluctuations areillustrated along with species diversity (H’) in Figure 31. As with theBowen Island comparison, the fluctuations in mean Fucus height diversityare quite synchronous with mean species diversity (H’) on a seasonal basis.Regression analysis of the pooled seasonal values revealed no significantcorrelation between Fucus height diversity and species diversity (H’).Multiple regression analysis (UBC BND:02R) was incorporated to determinewhich independent variables were most important in affecting speciesdiversity and the total numbers of organisms (Table 3). The dependentvariables (H’), (H), and numbers of organisms were transformed logarith-mically (base 10) to reduce variations from northality. No clear trendsemerged from this analysis when all the seasonal data are pooled. Theindependent variable, number of dichotomies perunit length of Fucus, wasmost important, accounting for 10.25% of the variation in (H’) and 10.12%36of the variation in (H). The dry weight of Fucus was associated witha reduction of 5.15% and 4.54% of the variation in (H’) and (H)respectively. The number of dichotomies per plant contributed to mostof the variation in numbers of organisms, 13.79%, with 10.97% beingaccounted for by the number of dichotomies per unit length of Fucus.Seasonal separation of the data into Spring, Summer, and Autumncomponents and subsequent application of multiple regression analysisled to the results summarized in Table 7. The change in mean substratediversity is shown in Figure 21. Multiple regression analysis of thesubstrate diversity and number of organisms yielded no highly correlatedassociations.Meaningful results could not be obtained from recordings ofpositions of organisms on individual plants because of the often sparsefauna and the tendency of Mytilus edulis to dominate on the plants. Thedistribution of Mytilus is shown for plants 0—10 cm in height and plantsgreater than 10 cm in height (Figure 32). Approximately 92% of theMytilus were attached to the lower portion of the stipe (0—3 cm from theholdfast) on plants ranging in size from 0—10 cm. The Myilusdistribution on plants greater than 10 cm is more variable than on plantsless than 10 cm in height with the maximum numbers again occurring nearthe holdfast but with a secondary maximum occurring at 5 cm.k) Mytilus—Fucus Competition (Juvenile Plants)The detrimental effect of M. edulison the growth of juvenileFucus plants was established through Mytilusremoval experiments. Forone replicate experiment, the growth rate of those plants cleared of37M. edulis was similar to those plants with Mytilus left intact forapproximately 23 days (Figure 33—B). After this time however, Mytilusovergrew the plants that were not cleared of Mytilus and subsequentgrowth of these plants was not evident. The plants removed from theinfluence of Mytilus grew a further 3.08 cm (mean of 6 plants) in 71 days.Similar results were obtained with a second group of six plants where nofurther increase in growth of those plants with Mytilus was evidentafter 48 days (Figure 33—A). The mean increase in growth of plantscleared of Mytilus after the 48 days was 8.35 cm.1) Mytilus—Fucus Competition (Adult Plants)The growth and survival of larger plants was also improved in theabsence of Mytilus. Growth rates of plants cleared of Mytilus could not becompared with plants influenced by Mytilus because after approximatelythree weeks, all plants with attached Mytilus had become “fused” to therock substrate and the surrounding Mytilus bed. Characteristically, a fewMytilus individuals on the plants would attach via their bysall threads toother mussels on the rock surface. Other mussels would then attach alongthe length of the plant and eventually cover the entire plant leading tothe eventual death of the plant. Plants cleared of Mytilus did not sufferthis fate, but rather, they continued to grow and develop. The plantscleared of Mytilus grew a mean height of 8.17 cm in 2.5 months.A secondary effect of Mytilus on Fucus was noticed whereoccasionally large Fucus plants could be seen extending from extensiveMytilus clumps. Examination of some of these plants revealed that theirholdfasts were clear of the substrate and the plants were being supported38by attachment of the mussels. Presumably, the pressure exerted bythe mussel bysall threads under the influence of wave force, forced theholdfast from the substrate. This hypothesis was tested in thelaboratory and is discussed later.m) Limpet Marking ExperimentLimpet migration out of areas cleared of Fucus wassignificantly greater than from areas of intact Fucus stands. Theresults for 3 experimental trials are shown in Table 8. In May, 1973,32 of 60 marked limpets remained in the Fucus area after one week whileonly 8 of 43 original marked limpets remained in the cleared area. Ofthose marked limpets originally in the cleared area, 5 had migrated intothe adjacent Fucus area. A test comparing the proportions remaining ineach area (Ho: the proportion remaining in the cleared area proportionin uncleared area) was carried out by calculating a value (Woolf,1973). The c value (Table 8) is 4.0 at p < 0.001 so the null hypothesisis rejected; the proportion of limpets remaining in the intact Fucus areais significantly greater than that of the cleared area. The experimentwas duplicated in June with smaller numbers of limpets and similar resultswere obtained. After 27 days, 6 marked limpets of an original 10 remainedin the Fucus area along with 2 that had migrated in from the cleared area.Only one marked limpet of an original 10 remained in the cleared area.After two months 8 marked limpets could be found in the Fl4cus area with 4of those having originated in the cleared area while no marked limpetsremained in the cleared area. The third duplication (Table 8, trial 3)yielded similar results to the two previous trials.39n) Laboratory Experimentation(I) Behavior ExperimentsLaboratory behavior experiments dispelled a theory of threeinvertebrate species being able to chemotactically locate Fucus. NeitherLittorina sitkana nor L. scutulata reacted positively to the presence ofFucus. The littorinids dispersed towards the sides of the experimentalapparatus with no apparent tendency to distribute themselves on eitherside. With a sample of 50 L. sitkana averaged over 10 replicate trialsthe mean number of L. sitkana found on the Fucus side of the tank was 19.8with 22.1 being found on the control side. Analysis of variance showedthe mean numbers on each side did not differ significantly (Table 9).Similar findings were obtained using L. scutulata. Of 7replicate trials the mean number of L. scutulata found on the Fiicus sidewas 22.8 with 25.8 individuals being found on the control side. Analysisof variance again revealed that no significant difference between thenumbers found on each side existed (Table 9).Acmaea pelta did not migrate in significant numbers to eitherside of the tank but, rather, tended to remain clumped in the center ofthe tank or clumped to each other such that meaningful analyses of theirresultant distributions could not be made.(II) Idothea Selection ExperimentsThe experiments with Idothea to determine if the animalpreferentially selected algae of greater complexity suggests that Idotheadoes prefer plants with a greater degree of structural complexity. The40four types of plants used were ranked from level 1 (most structurallycomplex) to level 4 (least structurally complex) in the experiments.Using 10 Idothea in the first experimental series, the animalsaggregated on the most complex plants (level 1, Figure 34—A). With 4trials combined, 22 individuals were found on the level 1 plants, 6 onlevel 2, 6 on level 3, and none on level 4.Similarly, using 15 Idothea per trial there was a noticeabletendency for the animals to distribute themselves on the most complexplants (Figure 34—B). Of a total of 4 trials combined, 40 were found onlevel 1, 9 on level 2, 1 on level 3 and none on level 4. When 25 Idotheawere used per trial, similar distributions were found (Figure 34—c).The cumulative total for 6 trials was 98 individuals on level 1, 19individuals on level 2, 9 on level 3, and 2 animals on level 4. Chisquare analysis indicates the significant tendency ofIdothea to selectplants of the greatest complexity (Table 10).(III) Pagurus GrazingLaboratory observations of Fucus in the presence of hermit crabssuggested that Pagurus can impose extensive grazing pressure on juvenilefucoids. Following submersion in the presence of Pagurus, all the Fucusplants displayed characteristic grazing marks similar to those found onplants apparently grazed by Pagurus in the field. The edges of the frondsappear serrated (Figure 27) when compared with ungrazed plants. Smallerplants were often completely grazed from the rock surface. Examination ofPagurus fecal pellets revealed cells which resembled Ftcus cortex cells.41(IV) Pisaster—Fucus InteractionsThe field experiment designed to test the hypothesis ofPisaster—induced mortality of Fucus attached to Balanus glandula wasduplicated in the laboratory with similar results. After two weeks50 of the 54 (92%) Fucus plants attached to Balanus were removed byPisaster preying on the substrate barnacle. None of the 50 Fucus plantsattached directly to the rock surface suffered any mortality. Theexperiment was replicated five times with the mortality of Fucu attachedto Balanus being greater than 90% for each trial. No mortality of thoseFucus plants attached directly to the rock surface was evident.(V) Mytilus Removal of FucusAfter a two month period 11 of the 70 plants (15%) had beenremoved from the substrate presumably from pressure exerted by the mussels.All the plants removed were small (0—5 cm) with none of the larger plantsbeing removed.42DISCUS S IONa) Diversity and Community StructureAssociated with intertidal populations of Fucus is a faunalcommunity which varies in diversity both seasonally and spatially. Someof the animal genera found on Fucus are similar to those recorded inother studies, e.g., Idothea and Littorina, (Lewis, 1964); Hyal,(Wieser, 1952; Bousefield, 1957; Lewis, 1964). The diversity of thefauna of the two study areas as expressed by (H’) differed with thefaunal diversity on Bowen Island being generally greater than atLighthouse Park although the types of organisms found in both areaswere similar. The relative contribution of fluctuating populations ofanimals such as amphipods on Bowen Island was to increase faunaldiversity during times of population peaks. The lack of distinctfluctuating populations of organisms at Lighthouse Park tended to reduceoverall diversity.Seasonal fluctuations of the fauna associated with Fucus havebeen noted by other researchers (Haage and Jansson, 1970; Hagerman, 1966).Generally, in these studies lowest numbers of organisms were found in thewinter months and maximum numbers in the summer months. The causalfactors operating behind the fluctuations are probably those which affectall intertidal populations, i.e., high winter mortality and maximumrecruitment of the populations in spring and summer. The use of Fucusin the summer months as a refuge from environmental stresses, such as hightemperatures, may contribute to the increased numbers of certainorganisms found associated with the alga in this season. Fucus tends to43trap water among its fronds and this action, coupled with naturalexudation maintains a humid, relatively cool environment. Periodicmeasurements of temperature taken with a thermometer placed among thefronds of Fucus showed temperatures of up to 5°C below air temperature.The environment found among Fucus fronds during summer is probably afavored environment for certain organisms such as amphipods.When the diversity values over thá total sampling period forBowen Island are pooled, multiple regression analysis suggests arelationship between the number of plant blade dichotomies per quadratand animal species (H?) and diversity per individual (H). The low degreeof correlation however (R2 = 16.41 (H’) and R2 = 21.02 (H)), is the resultof tremendous temporal and spatial variation. This relationship issimilar to the trend noted in terrestrial communities of increasing insectspecies diversity with increasing plant structure (Nurdoch, Evans, andPeterson, 1972). An increase in the degree of dichotomization of a plantresults in an increase in the 3—dimensional structure of the plant. Suchan increase in structural complexity may act to separate populations ofpotentially competitive species. The numbers of individual organisms,unlike species diversity, is more closely associated with the totalcumulative height of the plants per quadrat. The total amount of physicalspace in terms of total length may be more important than the amount ofpartitioning of that space through dichotomization with respect to thetotal numbers of organisms found.The importance of the degree of dichotomization is alsoapparent at Lighthouse Park where the number of dichotomies per unitlength accounted for most of the variation in (H’) and (H) with the44number of dichotomies per plant accounting for most of the variationin the total numbers of individual organisms. Fucus height diversitywhen averaged for each sampling period is synchronous with changes inmean animal species diversity (H’) which suggests the importance ofstructural complexity (e.g., MacArthur’s foliage height diversity,MacArthur, 1965) in contributing to species diversity.The trends established with the pooled data are not apparentwhen one considers the seasonally partitioned data. The lack of a clearseasonal trend might imply that those factors governing or affectingcommunity structure are not continual seasonally but vary over time.Thus at any specific time, no primary causal factor could be predictedas the one contributing most to the. resultant faunal species diversity.The question of why species diversity on Bowen Island ishigher than at Lighthouse Park remains unanswered and is open tospeculation. One reason may lie in the differences between the relativemortality rates of populations of invertebrates in both areas. LighthousePark, relative to Bowen Island, could be considered an area of greaterstress in terms of the amount of physical damage incurred on the biotathrough storms and drift logs. Although not measured, damage to theintertidal biota from drift logs at Lighthouse Park is probably considerable,a supposition supported by previous studies in the area (Ross and Goodman,1974). The action of these logs would be to physically remove largenumbers of organisms from their substrate. Dayton (1971) considers logdamage a major contributing factor in the creation of “open spaces” in theintertidal zone.45One factor which may determine the types and numbers oforganisms found associated with Fucus is the so—called whiplash effect(Lewis, 1964), whereby Fucus under the influence of wave pressure tendsto dislodge or prevent barnacles and other organisms from settling onthe substrate. Presumably the whiplash effect would be greater in areasof greater exposure and may tend to prevent the settlement or attachmentof forms which might normally be present in less exposed areas. Hence,at Lighthouse Park there may be a physical interference phenomenonoccurring which is not apparent at the less exposed Bowen Island site.The decreased diversity at Lighthouse Park could also be due togreater recruitment and survival of Mytilus edulis, and the formation of asingle species complex. Harger and Tustin (1973a) suggest that two groupsof factors can influence the successional patterns in marine communities.The first is the availability of colonizing organisms and the second isthe structure of the resident community. The presence of a largepopulation of Mytilus may prevent establishment of further species throughcompetitive exclusion which serves to maintain a simplified assemblage oforganisms on Fucus. The phenomenon of Mytilus becoming competitivelydominant in the intertidal zone is described by Paine (1966, 1974). Inthe absence of predators Mytilus californianus dominated the intertidalzone resulting in the elimination of up to 25 macroscopic invertebratespecies.The nature of the substrate to which Fucus is attached may alsoplay a role in determining the types of animals found on the alga.Typically, Fucus is found growing on large rock masses in the intertidalzone in the study area at Lighthouse Park whereas on Bowen Island, Fucus46abounds on small boulders. The fauna I found associated with Fucus isnot unique to the alga but rather, is commonly associated with under—rockand crevice habitats. For example, the hermit crab Pagurus is commonlyfound in crevices, tidepools, or under rocks. On Bowen Island, Paguruscould readily be found among Fucus which was growing on small rocks. AtLighthouse Park however, the only Pagurus found associated with Fucuswere located in crevices or tidepools. Similarly, Hyle and Idothea arecommonly found in an under—rock habitat. Populations of fucoids growingon cliffs and very large boulders do not have a large potential source oforganisms which could emigrate from an under—rock habitat to aFucushabitat. Peaks in the abundance of organisms associated with Fucus onBowen Island may be the result of dispersion from “natural” habitats due tointer— and intraspecific interactions in space or food—limitations. Thesubsequent decline in numbers associated with Fucus in winter months maybe a function of decreased competitive interactions resulting from wintermortality which tends to decrease dispersal pressure from natural habitatsto Fucus habitats.Another consideration may be linked with the structure of theFucus pse. Substrate complexity or diversity, both on a macro— andmicroscale has been considered to be an important attribute in determiningthe chain of successional events from initial colonization to a diversecommunity (Seed, 1969; Bayne, 1965; Harger and Tustin, 1973a).Differences in the microtopography of the surface of Fucus frond may inturn result in different species associations or differences in the ratesof colonization. For example, Fucus at Bowen Island contained manyprominent caecostomata which tended to increase the surface complexity of47the alga. Also, the degree of exudation may contribute to the presenceor absence of certain forms such as Hyale. Mytilus edulis larvae havebeen shown to prefer filamentous surfaces on which to attach (Bayne,1965). Fucus at Lighthouse Park is often found with considerable amountsof the epiphyte Elachisteafusicola, the filaments of which may serveas attachment sites for Mytilus larvae.A final consideration of differences in diversity between thetwo study areas involves the palatability of Fucus in both areas.Recently, much effort has been directed towards substantiating the roleof metabolic substances as chemical defense mechanisms against predationin higher plants (Levin, 1971; Janzen, 1969). Vadas (1968) suggeststhat the benthic alga Agarum, has evolved a chemical defense system whichacts to “... effectively reduce the incidence of grazing...” The presenceof Idothea and signs of grazing at Lighthouse Park tends to disfavour thishypothesis for juvenile plants. Many larger, mature plants however, arenever found with any associated organisms or visible signs of grazingeven though many organisms can be found on nearby plants. This suggestspossible age specific differences in the palatability or “attractiveness”of the plants to organisms.Deriving relationships between measurable structural features ofintertidal algae and associated faunal communities presents a majorproblem in terms of the high degree of variability which prevails betweenlow and high tides. At low tide the plants assume a static positionwhich comprises a specific volume of space. At high tide the plant issubject to wave and current forces such that the position maintained byany given plant varies considerably. In light of these constraints in48defining the position and volume of space occupied by the plant it isdifficult to apply the same measures of vegetation structural diversity ashas been done with higher plants. Of importance to the question ofwhich component of algal structure is most highly correlated with animalspecies diversity and community structure is the timing over a tidalcycle with which motile animals can establish themselves with aparticular Fucus plant. Diving observations over Fucus beds at high tiderevealed that motile species move freely among the Fucus fronds. Hyale,Idothea, Pagurus and Gnorimosphaerorna were often seen swimming about theplants. Selection for specific plants or groups of plants by thesespecies would probably occur as the tide ebbed with the animals remainingaffixed to the plants they selected throughout the low tide period. Otherforms such as Littorina sitkana and L. scutulata become associated withthe alga once the tide has fallen and they are able to disperse among thefronds. Two forms of colonization then,are apparent. These are:1) selection by highly motile forms, e.g. Idothea2) ‘Passive’ selection by “erratic” dispersers, e.g. Littorina.Unlike investigations of terrestrial plant—animal associationswhere active competition and resource partitioning is thought to lead toa division of the habitat and coexistence (MacArthur, 1958, 1965)competition among the forms on Fucus is minimized by environmentalvariability (high and low tides) and the role of Fucus as a refugerather than a food source for most forms. MacArthur (1965) summarizesthe theory of within habitat diversity stating that the number of specieswithin a habitat can be expected to increase with habitat productivity,structural complexity, lack of seasonality of resources, the degree ofspecialization, and reduced family size. An increase in structural49complexity of Fucus on Bowen Island would probably not result in anincrease in species diversity. In terms of the species pool availableon Bowen Island, those forms presently found on Fucus represent thespecies complement which is able to colonize the alga. An increase inthe diversity of potential colonizers would be required to increasethe diversity of the Fucus associated fauna.The results from the individual Fucus transplant experimentssuggest that the motile fauna associated with Fucus is highly transient.Rapid colonization of the individual plants was followed by fluctuationsin mean diversity levels regardless of the density of the Fucus zone intowhich the plants were placed. Thus a “climax” fauna is not established,at least over the time period the process was observed. The structureof individual plants over the range of variation tested did not influencethe diversity of the colonizing fauna which suggests that the structureof groups of plants is more likely to determine the nature of theassemblage of organisms found therein. The diversity of the fauna whichcolonized groups of plants differed between areas of low density Fucusand areas of high density Fucus but within each area the diversity measuredover time was similar for groups of plants with more than 10 individualsper group and groups with fewer than 10 individuals. The number of plantsrequired for maximum diversity to be attained on bricks 23.0 cm x 15.0 cmx 8.0 cm is less than 10 plants. Areas of high density Fucus arepreferable to low density areas and may be selected by certain organisms.Idothea for example, was shown to clearly select plants of greatercomplexity in the confines of an aquarium tank. On a larger, natural scale,Idothea would probably select areas of dense Fücus because such areas would50represent optimal feeding sites and superior refugia. The importanceof density was established from the density transplant experiments.Differences in diversity between areas of high and low density Fucusimplies there is some selection by motile forms for areas of dense Fucus.The results of lab experiments designed to test the ability ofLittorina sitkana, L. scutulata, and Acmaea pelta to locate food sourcesagrees with results in other experiments. Behrens (1971) concluded thatL. sitkana is not able to chemotactically locate food. Although thepresence of Fucus did not influence the growth rate of Acmaea orLittorina, the limpet marking experiment indicates that Acmaea utilizesFucus as a refuge, probably against heat stress and predators. Southward(1964) suggests that limpet growth is enhanced in a favorable and damphabitat such as that found under a Fucus canopy.The distribution of the dominant organisms on individual Fu.gusplants is shown to vary with the height of the plant. This variation isprobably a result of increased plant contact with the substrate providedby taller plants and is not the result of selection of specific portionsof the plant by particular organisms. The tendency of Mytilus to bedistributed near the holdfast in all size categories of plants except forthe largest at Bowen Island may be the result of Mytilus crawling from thesubstrate up the stipe of the plant and attaching near the base of theplant. On larger plants Mytilus probably attaches to the plant when thefronds of the plants are lying prostrate over a population of mussels.At Lighthouse Park the distribution of Mytilus on Fucus tends to beclumped toward th base of the plants on all sized plants. This could bethe result of the “whiplash” effect described earlier which would prevent51establishment of Mytilus on the outer extremities of the plant. Accessto shorter plants by littorinids is gained by crawling up the stipewhile access to taller plants is obtained by moving onto the fronds whenthe plant is lying flat on the substrate.b) Lower Intertidal Distribution of FucusSome of the earliest studies of Fucus emphasized the role ofphysical factors in determining the vertical intertidal distribution ofFucus. Gail (1918) concluded that “light is a controlling factor indetermining the lower limit of Fucus”. Zanveld (1937) emphasized theeffects of desiccation as a primary controlling factor in intertidalalgal zonation which have been re—emphasized recently by Bdrard—Therriaultand Cardinal (1973) who stressed the role of desiccation in determiningvertical distributions of the Fucaceae. McLachlan (1974) suggests thatthe lack of Fucus in the sublittoral zone could be the result of a lackof colonization by embryos. Although the ultimate lower limit of Fucusis probably determined by physical factors, the potentially realized lowerdistribution in the intertidal zone is determined by biological interactions. No single factor however, can be said to be responsible for anoted distribution but rather, more than one factor may be operating inone area. Those major factors which seem to control, in part, the lowerlimits of Fucus on Bowen Island and Point Atkinson are as follows:(1) Pisaster—induced mortality. As my field and laboratory results haveshown, Pisaster can, through predatory activity on those barnacles towhich fucoids are attached, disengage the plants from their substrate whichresults in death to the removed plants. The upper limits of Pisastermigration coincides remarkably with the lower limits of Mytilus edulis and52the Fucus zone. Barnacles, B. glandula, in the lower intertidal zonedid not attain a size greater than two or three millimeters in diameterpresumably because of repeated predation by Pisaster. Above the Pisasterzone barnacle sizes vary from newiy settleu forms to large (5—6 mm indiameter) forms suggesting an age class distribution from one to a fewyears.(2) Competitive inhibition by Mytilus edulis. Mytilus can kill Fucusby smothering or by removing the entire plant from its substrate. As thefield experiments have shown, the growth of Fucus is effectively curtailedthrough the smothering effect of Mytilus. The ability of N. ëdulls tocrawl CHarger, 1970) gives the mussel a competitive advantage overpermanently attached forms such as Fucus. Mytilus may cause mortalityto Balanus glandula by overcrowding and eventually suffocating them(Ross and Goodman, 1974).(3) Grazing by Pagurus. Most species of intertidal hermit crabs aregeneralized feeders, feeding on a variety of dead and decaying plants andanimals (Vance, 1972). On Bowen Island Pagurus assumes the role of ahervivore for at least part of the year and effectively reduces the growthof Fucus in the lower intertidal zone. Field and laboratory experimentsshow that Pagurus can extensively graze on Fücus, primarily the juvenileforms. Such grazing can either retard growth or kill small fucoids. Aninteresting unanswered question concerning hermit crab grazing is whygrazing is only prominent in the late summer months. One possible reasonmay be the result of seasonal differences in aspects of the biochemistryof the plant which renders it more palatable in late summer. A secondpossibility may be that the end of summer marks the end of preferred food53sources of the hermit crab such that the animal is forced to feed onFucus. Such hypotheses require further investigation.c) Fucus Characteristics at Bowen Island and Lighthouse ParkThe differences in characteristics of plants from LighthousePark and Bowen Island may be the result of differences in the degree ofexposure between the two sites. Increased wave action has been shownto decrease vesiculation in Fucus vesiculosus and decreased salinity toincrease vesiculation and branching (Jordan and Vadas, 1972). Surfstrength and current speed significantly affected the growth anddevelopment of fucoids of the White Sea, with plants growing on siteswith a strong surf being longer and structurally stronger (Terekhova,1972). Knight and Parke (1950) suggest that exposure to rough watermay accelerate dichotomy of F. serratus. The increased wave action atLighthouse Park may account for the larger size and greater numberof dichotomies found than at Bowen Island. To validate this hypothesiscontrolled transfer experiments are required. The presence of an upperintertidal form which is reproductive in winter on Bowen Island issimilar to the situation on the Atlantic Coast where F. edentatus andand F. distichus form mature receptacles during winter (McLachlan, 1974).54SUNMARYIntertidal Fucus populations at Bowen Island and LighthousePark have an associated faunal community which varies seasonally interms of the abundance of organisms and the diversity of the animalassemblage as expressed by the indices (H’) and (H). Multiple regressionanalysis indicated that the degree of algal dichotomization is associatedwith a considerable portion of the yearly variation in animal speciesdiversity. When analyzed on a seasonal basis, different variables aremore strongly correlated with species diversity at certain times ofthe year. These variables are plant height diversity, quadrat position,mean number of dichotomies per plant and mean height per plant.Differences in animal species diversity observed between the two studysites may result from differences in algal structure, algal palatability,the degree of wave exposure, the type of substrate on which the plantsare attached, and competitive exclusion processes.Biological interactions were found to control, in part, thelower intertidal distribution of Fucus. These interactions include:(1) Predatory activity by Pisaster ochraceus on barnacles to whichplants are attached which results in plant mortality.(2) Seasonal grazing by hermit crabs which kills plants or reducestheir growth.(3) Competition for space with Mytilus edulis which results in thesmothering and eventual death of Fucus plants.55LITERATURE CITEDBayne, B.L. 1965. Growth and delay of metamorphosis of the larvaeof Mytilus edulis. Ophelia 2(1): 1—47.Behrens, S. 1971. 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Food web complexity and species diversity.Am. Nat. 100: 65—75.58Paine, R.T. 1971. A short term experimental investigation ofresource partitioning in a New Zealand rocky intertidal habitat.Ecol. 52: 1096—1106.Pianka, E.R. 1967. On lizard species diversity: North Americanflatland deserts. Ecol. 48: 33—351.Pielou, E.C. 1966. Species diversity and pattern diversity in thestudy of ecological succession. J. Theoret. Biol. 10: 370—383.Pollock, E.G. 1969. Interzonal transplantation of embryos andmature plants of Fucus. Proc. 6th. mt. Seaweed Symp.,p. 345—356.Powell, H.T. 1963. Speciation in the genus Fucus L., and relatedgenera. In: Speciation in the sea. Systematics AssociationPubl. No. 5, Làndon. p. 63—77.Ross, J.R.P. and D. Goodman. 1974. Vertical intertidal distributionof Mytilus edulis. The Veliger 16: 388—395.Scagel, R.F. 1959. The role of plants in relation to animals inthe marine environment. 20th. Ann. Biol. Colloquium, OregonState College, Corvallis, p. 11—29.Seed, R. 1969. 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Ecol. 25: 431—469.60Figure 1Map of Bowen Island showing study area.62Figure 2Map of Point Atkinson showing study area at Lighthouse Park.6364Figure 3Diagrammatic representation of Fucus attachment to a cement block.Ln“C66Figure 4Experimental cages used in littorinid and limpet growth experiments.67In- t;4—b:--I68Figure 5Experimental apparatus used in laboratory experiments withLittorina and Acmaea.I—-acIwn6970Figure 6Frequency distribution of plants heights at Bowen Island (a)and Lighthouse Park (b).C C In I m H I -1‘1 C C U.) I rq H C, I -1NO.OFPLANTSorNO.OFPLANTS(00•72Figure 7Frequency distribution of number of dichotomies per plant at BowenIsland (a) and Lighthouse Park (b).SINV1ddO-ONIz-J0ILl0InILl1-4DI—CIf-i1-4CEz-J0EdaLflEd1-4aaIUI-IC-8-2a.uja.0.1•IIT1IIIILf0S.LNV1ddO-ON74Figure 8(a) Regression of Fucus height against number of dichotomiesat Bowen Island. Regression equation: Y = 0.132 + 0.344X(b) Regression of Fucus height against number of dichotomiesat Lighthouse Park. Regression equation: Y = 0.213 + 0.296XComparison of the slopes of the two regression lines yielded asignificant difference at p=O.O5 (F6.l4) and comparisonsbetween adjusted means at X=7.385 yielded significant differencesat pO.OO1 (F=15.97).DICHOTOMIES(SQLURERDDT)DICHOTOMIES(SQUARERWT)T1 C C In r m z G) H I-9 n C v-i I m z H Ix‘C‘C XX‘C‘C‘C XX‘C‘C‘CX‘C X‘C‘CXX‘C‘C‘CXXXXcJl76Figure 9(a) High intertidal form of Fucus from Bowen Island, reproductiveJanuary, 1974.(b) Mid intertidal form of Fucus from Bowen Island, reproductive,July, 1974.F,SCt078Figure 10Diagrammatic representation of an individual Fucus plantattached to Balanus glandula with some of the most commoninvertebrates found associated with the alga.4479Lco4l.Iye u,oSaJA.4-ez.•Nf.t14; 1j80Figure 11Changes in the number of Littorina sitkana on Fucus per quadrat,Bowen Island, from May 1973 to late July 1974, (a), andLighthouse Park, (b). Each sampling interval represents approximately1.1 months for this and all subsequent plots of this type. Thecurve represents a third order polynomial fitted by the methodof least squares.81i3D.cO (a)x.< 12J.cXJ< ilO.cOxim.ajLfl X93.03c 70.cOI—I—X Xx- 5j.O xXx x410.03 xxxciJqjzio.co0.030.0 i.0 2.0 3.0 4.0 5.0 E.O 7.0 8.0 S.D 10.0 1.1.0 12.0 13.0 1.4.0MAY’73 OCT.’73 APR.’74 JUL.’74SAMPLINL INTERVAL33.03 (,1))x.0OI—I-1U.,-4I-4-J 10.03xI..CD‘CxuJxQ.03 XIX I.0.0 1.0 2.0 3.0 4.0 5.0 G.O 7. 8-0 S.O 10.0 11.0 1.2.0 13.0MAY’73 SEPT.’73 JUL.’74SAMPLING INTERVAL82Figure 12Changes in the number of Littorina scutulata on Fucus per quadrat,Bowen Island (a) and Lighthouse Park (b).83(a)-JxLfl XLa..xxbJ Xxxxxx xO4X X X XXt X—t XQ I I I IX I I0.0 i.0. 2.0 30 4.0 5.0 6.0 7.0 8.0 S.O 10.0 11.0 12.0 13.0 i4.0MAY’73 OCT.’73 APR.’74 JUL.’74SAMPLING INTERVAL(b)XI—9.y3xU-JLa..x3.cyJ0.xxx0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9O 10.0 11.0 12.0 13.3MAY’73 SAMPLITdTERVAL JUL.’784Figure 13Changes in the number of Mytilus edulis on Fücus per quadrat,Bowen Island (a) and Lighthouse Park (b).85xx(a)41c0.003DOO200.00i5O.cY3[000E00.00xxx‘C x0.0 1.0 2.0 3.0 4.0 5.0 8.0 7.0 8.0 9.0 10.0 il.O 12.0 13.0 iA.OMAY’73 OCT.’73 APR.’74 JUL.’74SAMPLINE3 INTERVAL(b)x‘C700.0050003400.0030.00i00Ox ‘Cf-n-4-JCDu.-4>-CDUicx‘C0.00‘Cx0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 jj.3 12.0 13.0MAY ‘73 SEPT.’73 JUL.’7SAMPLING INTERVAL86Figure 14Changes in the number of aniphipods on Fucus per quadrat, BowenIsland (a) and Lighthouse Park (b).8753.03 (b) a)xx0C-..c 75.0353.03w0.00MAY’73‘Cxxxxx‘Cxxxx1.0 2.0 3.0 4.0 5.0 G.0 7.0 8.0 - 10.0 il.0 2.0 13.0 i4’OOCT.’73 APR.’74 JUL.’74SAMPLINt3 INTERVALa.,’ ..i I I XI I- I I I0.0 1.0 2.0 2.0 4.0 5.0 8.0 7.0 8.0 g. 10.0 il.O 12.0 5.3.0MAY’73 SEPT.’73 JUL.’74SAUPLINI3 INTERVAL88Figure 15Change in mean species diversity (H’) per quadrat (triangles)and Fucus height diversity (crosses), Bowen Island.I‘Sz4<wJUL. ‘74892”:MAY’73SAMPLING INTERVAL90Figure 16Changes in the mean number of animals on Fucus per quadrat atLighthouse Park (crosses) and Bowen Island (triangles).u-iJHz1<LICaa[tiSAMPLING INTERVAL91350.MAY’73 JUL.’7492Figure 17Regression of species diversity (H’) against Fucus height diversityfor Bowen Island. The regression is significant at pO.OO1 (F14.33),and the probability of the slope being zero is less than 0.001.93>-I-HI’)w>HaX KxKXXK,<‘kKXX KxKX <x 3XXXXXXKXXKXXCInwHUwU)KXKXX x xXKK‘IX’xKXXKxOeOx.5 3.0FUCUS HEIGHT DIVERSITY (H’)94Figure 18Frequency distribution of numbers of Littorina sitkana on plantsat Bowen Island.(a) Plants 0—5 cm in height. No. of plants = 35.(b) Plants 5—10 cm in height. No. of plants = 90.Cc) Plants 10—15 cm in height. No. of plants = 51,Cd) Plants 15—20 cm in height. No. of plants = 29,Ce) Plants > 20 cm in height. No. of plants = 7.NUhCR1OPI..1Z?IIAWANuMBERSorL.SZTRANA9,e•0 2 n 2 0 2 0 r 0NUMBERSOFL•5ZTANA0 I.i -I 2 1) m ‘I 2 0 C I 0 r 0 ‘1 Inii r t0 B -I 2 n m ‘I—2 0 C I 0 I- 0 ‘I B -IB m U U U U U UCDNUMBERSOFL.SZTANANUMBERSCF,L.IXTRANAa 2 ‘I 2 0 C I C r 0 ‘I U) -I0 In -I 2 n ‘I 2 0 C I 0 rU U U U U U U UU Ii) •196Figure 19Frequency distribution of Hyale plumuibsa on individual plants,Bowen Island.(a) Plants 0—10 cm in height. No. of plants = 31.(b) Plants 10—20 cm in height. No. of plants = 27.Cc) Plants > 20 cm in height. No. of plants 5NUMBERSOFHYALEPLUMLJLOSA‘-ItJ,zU)rn‘I‘1 o, I-o >-0 ‘-4 U, -4 >. C-, m •7 0 I 0 r 0 ‘1 U, -4ru U, U! a) a) 4- U) 4--mNUMRSFHALPLUMULSA94-PiU).Lfla)“Ca)—)IIêIII’II11II‘HI0 rINUMBERSOFHYALEPLUMULOSA0 (n -I z C-) 1 z 0 -n >98Figure 20Frequency distribution of Mytilus edulis on individual plants,Bowen Island.(a) Plants 0—5 cm in height. No. of plants = 24.(b) Plants 5—10 cm in height. No. of plants = 35.Cc) Plants 10—15 cm in height. No. of plants 32.Cd) Plants > 15 cm in height. No. of plants = 18.-49z ri‘I 10otnbi8•t•1I•I—IC I-I U) -1 > 0 m •1 0 r C ‘1 > U, -4NUMBERSOFM.EOULISNUMBERSOFM.COULtS0UI880I•II’H_____-49> ZLfl-I,;>;NUMBERSOFM.EOULXS-5C-)NUMBERSOFM.LOULZSotn880•IIII•IIIIIH cj,—49>;—I0)0.100Figure 21Changes in mean species diversity (H’) of the substrate faunaon Bowen Island (crosses) and Lighthouse Park (triangles).SAMPLING INTERVAL101‘aJUL. ‘742.F-’.3:.1 jzwMAY ‘730. i’ 2. 3. 4. 5. 6. 7. 6. 9.102Figure 22Changes in mean species diversity (H’) of structurally differentplants transplanted into three different Fucus density zones.(a) Low density zone.(b) Medium density zone.Cc) High density zone.Cd) All zones combined.+ = low level of complexity plantsX = medium level of complexity plants=i.high level of complexity plants-I‘-4 In-.4‘-Im—I‘-4 in-I Cr’IflAN(H’)MEAN(H’)nMEAN(H’)MCAN(H’)ha a U)C-104Figure 23Changes in mean species diversity (HT) for groups of plantstransplanted into two Fucus density zones,(a) Low density zone.(b) High density zone.(c) High and low zones combined.= groups of more than 10 plantsX = groups of less than 10 plants.IzLUIzLuIzLu]105(a)TIME (VEEcS)( b)TIME CEE3cS( c)TIME (VuEDcS)106Figure 24Changes in mean number of organisms on Fucus for groups ofplants transplanted into two Fucus density zones.(a) Low density Fucus zone.(b) High density Fucus zone.= groups of more than 10 plantsX = groups of less than 10 plants107(a)ico.TIME (VIEEJcS7-Ii)J‘-4zLizUi75.U)I< iso.z i.tJ75z50.U.( b)2. 5. 7. 1.TIME ‘VEBSS)108Figure 25Regression of limpet length against limpet height for limpetsunder three experimental treatments.(a) Cages with no Fucus.Original Equation: Y= —0.104 + O.460XFinal Equation: Y= —0.132 + O.474X(b) Cages with a plant of medium complexity.Original Equation: Y= —0.325 + O.584XFinal Equation: Y= —0.108 + O.490X(c) Cages with a plant of high complexity.Original Equation: Y= —0.135 + O.462XFinal Equation: Y —0.123 + O.469X+ = original length—height relationshipV = final length—height relationship(a)VVVV *+ +VV+i.c0.E‘-IH-JUI—H109(b)i.c +0.E4v34J‘F0.0 I•0.0 05 jO i.5 2.0. 2.5 3.0LIMPET LENGTH (CM)o.od.s i.S E.OLIMPET LENGTH (CM)Cc)V+IHV0..5 j.O j.5LIMPET LENGTH (CM)110Figure 26General pattern of Fucus zonation on Bowen Island.:1’111112Figure 27(a) Photograph of Pagurus—grazed plant from laboratoryexperiment along with an individual Pagurus.(b) Pagurus—grazed plant from the lower intertidal zone, Bowen Island.114Figure 28Regression of Fucus height against growing time for mid intertidalplants (triangles) (Y = 1.877 + 1.566X) and high intertidal plants(crosses) (Y 2.606 + l.195X), Bowen Island.I—2:I.-’LiIfJ]DUDLiJUNE’73 J A SS A M P L I N G I N T E R,V A LOCT. ‘73115bK4’xx3ax116Figure 29Growth and dichotomization of 10 plants that settled oncement blocks on Bowen Island. Triangles illustrate theincrease in the number of dichotomies and the crosses showthe growth rate.S3tVOiOH.tcI—I>ILlzHzH-Ja1r)I—w.O‘ON‘WChV)HIMOeI9118Figure 30(a) Grazing marks from Idothea and an individual Idothea.(b) Comparison of grazed plants (left) and ungrazed plants (right)from Bowen Island. Two individual Idothea can be seensituated on the plant to the left.611q120Figure 31Changes in mean species diversity (H’) per quadrat (+) andFücus height diversity CX) at Lighthouse Park from May, 1973 toJuly, 1974.1213.02.QLIz4:Li0.00. je 2. . 4. 5.€3. 7. 8a 9’ ±0. jjc j2. i3MAY’73 JUL.’74SAMPLING INTERVAL122Figure 32Frequency distribution of Mytilus edulis on individual plantsfrom Lighthouse Park.(a) Plants 0—10 cm in height. No. of plants = 44.(b) Plants > 10 cm in height. No. of plants = 33:: (a) 123o.n275.J2.ZILiiLi. 175.iEe.WI00.Dzso.6. 7 8. 8. 10.0.(b)ax.(fl 75•I-4CLiiLi. 175.a(J ISO.DISTANCE FROM HOLOFAST COAl124Figure 33Mean growth rate of two groups of 6 plants cleared of Mytilus(crosses) and two groups of 6 plants left with their Mytiluscomplement intact (triangles).(a) Experiment 1.(b) Experiment 2.s. (a)i2.9.----r-----f--±--±--+-H--4--H---±- -0. jO. 20. 3). -40. 50. 50. 70 50. 90X).j10wj2043).j40.TIME (DAYS)125IIwUz[LI 3’0..(b)I(SIULzwTIME (t1AYS)126Figure 34Selection of Fucus plants by Idothea in the laboratory.(a) 10 Idothea per trial (4 trials combined)(b) 15 Idothea per trial (4 trials combined)Cc) 25 Idothea per trial (6 trials combined)0NO..OFZOOTHEAPRPLANTNO.OFZOOTHEAPERPLANT0§9II’IC-) C U) D -U r,m x I..-INOOFtOOTHAPERPLANT‘1 C C If) r x HU)C C Ii, C-, C ly-U r x HI01APPENDIXLevels of significance for the following tables areindicated as following:N.S. = Not significant**= p<o.ol=p<O.OO1128129Table 1Comparisons of structural characteristics of Fucus betweenBowen Island and Lighthouse Park(1) Mean height per plantGroup Mean Standard Deviation Sample Size FLighthouse Park 8.244 2.835 42 25.763***Bowen Island 5.479 2.945 89(2) Number of plants per guadratGroup Mean Standard Deviation Sample Size FLighthouse Park 30.125 22.257 42 1.571 N.S.Bowen Island 38.117 37.571 89(3) Number of dichotomies per plantGroup Mean Standard Deviation Sample Size FLighthouse Park 9.196 8.091 42 1.387 N.S.Bowen Island 7.315 8.739 89Table 2List of organisms found associated with Fucus 130and on the substrate under Fucus at Bowen Islandand Lighthouse Parkci)__4.J ci)Ct.—‘ ciiCO 4-)CO COC) CoC)Cl) 3‘-‘ — rx. tl)a) ci):i :iMytilus edulis X X X XLittorina sitkana X X X XLittorina scutulata X X X XHyale plumulosa X X X XAcmaea pelta X X X XAcmaea testudinalis scutum— X — XAcmaea persona — X— XBalanus glandula X X X XChthamalus dali - X - XIdothea wosnesenski X X X XPa gurus granisimonus X X X XPagurus hirsutiusculus— X X XHemigrapsus oregonensis X X X XHemigrapsus nudus X X X XEmplectonema gracile X X X XEmplectonema burgeri X X X XEulalia viridis — —— XGarypus sp.- X - -Notoplana natans — —— XOtotyphlonemertes sp. X X - XSyllis adamantea X X X XGnorimosphaeroma oregonensis X X X XParasitengona (mites) X X - XTrichopteran larvae X X X XHalacarinidae (mites) X X — -Chironomid larvae — X - XCyclorrhapha (diptera) - X - XStaphylinid beetles— X — XEncrusting bryozoans X — XX = Present (—) = AbsentTable3Relationshipsbetweenindependentvariablesanddependentvariables,speciesdiversityandtotalnumbersofindividualorganisms,onFucus1BowenIsland(SeasonalDataPooled)RankorderofIndependentVariablesplus%contributiontototalsumofsquaresIndependentVariableCode(Numberinparentheses)1Numberofplantsperquadrat2Totalheightofplantsperquadrat3Totalnumberofdichotomiesperquadrat4Meanheightperplant5Numberofdichotomiesperplant6Numberofdichotomies/totalheightofplants7WetweightofFucus8DryweightofFücus9Covervalue(%)10Distancealongtransect11PlantheightdiversityDependentVariableRegressionSumofSquares(%)(3)(10)(4)(7)(H’)16.415.803.362.0429.72(3)(10)(4)(9)(H)21.026.383.933.3236.08(2)(1)(10)(5)No.ofindividuals41.243.711.761.6050.702LighthousePark(SeasonalDataPooled)DependentVariableRankorderofIndependentVariablesplusRegressionSumofSquares(%)%contributiontototalsumofsquares(6)(8)(7)(5)(H’) 4Relationships between independent variables and dependent variables,species diversity and numbers of organisms, on Fucus, Bowen Island.The data has been partitioned into seasonal components.Dependent Rank order of independent variables plus RegressionVariable % contribution to total sum of squares S.S. (%)January(11) ((7) (8)(H’) 28.43 17.77 12.76 87.00(11) (7) (8)(H) 28.36 17.16 10.25 85.41(10) (1) (3)No. of 12.74 11.60 10.15 75.49individualsApril-Nay(10) (7) (3)(H’) 31.40 27.94 6.82 89.39(10) (7) (3)(H) 29.51 24.86 6.87 86.69(2) (3) (11) i 36No. of 38.24 16.88 12.67 88.36individualsJuly(5) (1) (2)(H’) 22.22 4.01 3.46 37.85(5) (9) (11)(II) 27.65 5.95 4.34 48.28(8) (11) (9)No. of 21.68 2.89 2.39 30.31individualsAugust(10) (9) (5)(H’) 14.06 11.03 9.36 71.05(10) (9) (5)(H) 14.14 9.88 8.40 74.22(2) (5) (3)No. of 75.26 4.26 1.95 91.39individualsSept.—Oct.(4) (11) (3)(H’) 78.27 14.58 6.98 99.82(4) (2) (3)(H) 80.25 11.67 7.96 99.87(4) (3) (2)No. of 62.38 25.82 11.66 99.86individualsContinued...Table 4 (Continued)Independent Variable Code1 Number of plants per quadrat2 Total height of plants3 Total number of dichotomies4 Mean height per plant5 Number of dichotomies per plant7 Wet weight of Fucus8 Dry weight of Fucus9 Cover value (%)10 Distance along transect11 Plant height diversity133134Table 5Analysis of variance comparison of final heights of Littorinasitkanafor three experimental treatments, no Fucus, medium complexity Fucus,and high complexity Fucus, Bowen IslandGroup Mean Standard Deviation Sample Size FNo Fucus 0.699 0.124 22 0.232 N.S.Medium 0.718 0.085 25High 0.705 0.101 40135Table 6Analysis of variance comparisons between final heights of matureplants transplanted to three intertidal sites, low, mid, and highintertidal, Bowen IslandGroup Mean Standard Deviation Sample Size FLow 17.900 3.928 3 0.959 N.S.Mid 21.083 3.917 6High 20.790 3.073 10136Table 7Relationships between independent variables and dependent variables,species diversity and numbers of organisms, on Fucus, Lighthouse Park.The data has been partitioned into seasonal components.Independent Variable Code1 Number of plants per quadrat2 Total height of plants4 Mean height per plant6 Number of dichotomies/totalheight of plants7 Wet weight of Fucus8 Dry weight of Fucus9 Cover value (%)11 Plant height diversityDependent Rank order of independent variables plus RegressionVariable % contribution to total sum of squares S.S. (%)Spring(H’)(H)No. ofindividualsSummer(H’)(H)No. ofindividualsAutumn(H’)(H)No. ofindividuals(6) (9) (7)20.72 11.52 6.92 66.38(6) (9) (7)19.52 10.25 8.84 66.10(9) (8) (6)25.86 17.66 15.60 76.60(7) (8) (4)40.22 31.51 12.31 99.85(8) (1) (4)39.02 26.46 19.55 99.95(2) (4) (1)71.65 9.58 7.33 99.93(4) (9) (1)46.10 30.83 9.59 98.51(11) (9) (6)42.42 28.30 15.41 98.61(1) (4) (11)36.84 36.80 15.86 98.51137Table 8Comparison of numbers of Acmaea pelta remaining on cleared anduncleared areas, Lighthouse Park.AreaExperiment 1 Clare4 UnclearedInitial No. 43 60Final No. 8 32 (+ 4 from clearedarea)“c”—value = 4.02**Experiment 2 Cleared UnclearedInitial No. 10 10Final No. 0 8 (+ 4 from clearedarea)Experiment 3 Cleared UnclearedInitial No. 10 10Final No. 0 5 (+ 6 from clearedarea)138Table 9.Analysis of variance comparison of numbers of Littorina sitkanafound on Fucus and No—Fucus side of experimental tank after 10 trialsGroup Mean Standard Deviation Sample Size FFucus 19.80 6.579 10 0.580 N.S.No Fucus 22.10 6.919 10Analysis of variance comparison of numbers of Littorina scutulatafound on Fucus and No—Fucus side of experimental tank after 7 trialsGroup Mean Standard Deviation Sample Size FFucus 22.85 5.815 7 0.905 N.S.No Fucus 25.85 5.984 7139Table 10Selection of structurally variable plants by IddtheawostiesenskiN=lO (Four trials combined)1 22 8.52 6 8.53 6 8.54 0 8.5Plant Level1234Chi—square = 30.917***Observed40910Observed98199Expected15151515Expected37.537.537.537.5Level 1Level 2Level 3Level 4Plants with more than 40 dichotomiesPlants with 20 dichotomiesPlants with 10 dichotomiesPlants with 0—5 dichotomiesPlant Level Observed ExpectedN=15 (Four trials combined)Chi—square = 72.12***N=25 (Six trials combined)Plant Level1234 2Chi—square = 16l.98***


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